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Human HeartHEART

is a squared shape, muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods

The Heart is divided into two

Right heart

Left heart

Right heart is a term used to refer collectively to the right atrium and right ventricle of the heart; occasionally, this term is intended to reference the right atrium, right ventricle, and the pulmonary trunk collectively.The right atrium receives deoxygenated systemic blood from the superior and inferior vena cavae. The blood is then pumped through the tricuspid valve into the right ventricle, which in turn pumps the blood through the pulmonary valve into the pulmonary artery.

Vena cavae, Coronary sinus→ Right atrium (auricle, fossa ovalis, limbus of fossa ovalis,

crista terminalis, valve of the inferior vena cava, valve of the coronary sinus) 

Tricuspid valve → Right ventricle (conus arteriosus, moderator

band/septomarginal trabecula)  Pulmonary valve→ Pulmonary Artery→ Pulmonary Circulation

Venae cavae The superior and inferior vena cava are collectively called the venae cavae. They are the veins that return de-oxygenated blood from the body into the heart. They both empty into the right atrium.

The superior vena cava (or anterior) is above the heart, and forms from a convergence of the left and right brachiocephalic veins that contain blood from the head and the arms. The vena cavae carry deoxygenated blood from the body to the right atrium of the heart.The venae cavae is the largest blood vessel in the heart.

The inferior vena cava (or posterior vena cava) travels up alongside the abdominal aorta with blood from the lower part of the body.

Coronary Sinus Coronary Sinus is a collection of veins joined together to form a large vessel that collects blood from the myocardium of the heart. It is present in humans and other animals.

LocationIt is located between the

left atrium and ventricle on the posterior surface of the heart.

It runs transversely in the groove between the left atrium and ventricle on the posterior surface of the heart.

The coronary sinus orifice (opening) is just superior to the septal leaflet of the tricuspid valve. The coronary sinus orifice is also known as the ostium of the coronary sinus

Right AtriumRight Atrium (in older texts

termed the "right auricle") is one of four chambers (two atria and two ventricles) in the human heart. It receives de-oxygenated blood from the superior and inferior vena cavae and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve.

Sinoatrial node (SAN) is located within this chamber next to the vena cava. This is a group of pacemaker cells which spontaneously depolarise to create an Action Potential. The cardiac action potential then spreads across both atria causing them to contract forcing the blood they hold into their corresponding ventricles.

Right VentricleRight Auricular Appendix

Fossa Ovalis

Limbus of Fossa Ovalis

Crista Terminalis

Valve of the Inferior Vena Cava

Valve of the Coronary Sinus

Right Auricular AppendixRight auricular appendix

(right auricula, right auricle) is a small conical muscular pouch attached to the right atrium of the heart. Its margins present a dentated edge. It projects from the upper and front part of the sinus forward and toward the left side, overlapping the root of the aorta.

Fossa Ovalis (heart)

Found in the right atrium of the heart, the Fossa Ovalis is an embryonic remnant of the foramen ovale, which normally closes shortly after birth. Failure of the foramen ovale to close results in a disorder known as patent foramen ovale.

Limbus of Fossa OvalisLimbus of fossa ovalis

(annulus ovalis)

is the prominent oval margin of the fossa ovalis.

It is most distinct above and at the sides of the fossa; below, it is deficient.

A small slit-like valvular opening is occasionally found, at the upper margin of the fossa, leading upward beneath the limbus, into the left atrium; it is the remains of the fetal aperture between the two atria.

Crista TerminalisIn the development

of the human heart, the right horn and transverse portion of the sinus venosus ultimately become incorporated with and form a part of the adult right atrium, the line of union between it and the right auricle being indicated in the interior of the atrium by a vertical crest, the crista terminalis of His (Wilhelm His, Jr.).

Valve of the Inferior Vena CavaThe valve of the

inferior vena cava (eustachian valve) serves to direct the blood from that vessel through the foramen ovale into the left atrium.

The eustachian valve is the valve at the distal end of the inferior vena cava the passes blood from the lower extremities into the Right Atrium of the heart

Valve of the Coronary SinusThe valve of the

coronary sinus (Thebesian valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of the coronary sinus. The valve may vary in size, or be completely absent.

It may prevent the regurgitation of blood into the sinus during the contraction of the atrium.

This valve may be double or it may be cribriform.

Tricuspid ValveTricuspid valve

is on the right side of the heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles.

Tricuspid ValveThe largest cusp is interposed between the atrioventricular orifice and the conus arteriosus and is termed the anterior or infundibular cusp. A second, the posterior or marginal cusp, is in relation to the right margin of the ventricle. A third, the medial or septal cusp, to the ventricular septum. The tricuspid valve prevents the blood from returning to the right atrium when the right ventricle contracts

***** The tricuspid valve also opens and closes at periods of time making the blood flow through from the right atrium to the right ventricle*****

Right Ventricle

Conus Arteriosus

Moderator Band/Septomarginal Trabecula

Right VentricleRight ventricle

is one of four chambers (two atria and two ventricles) in the human heart. It receives de-oxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve.

It is triangular in form, and extends from the right atrium to near the apex of the heart.

Conus ArteriosusConus Arteriosus

is a conical pouch formed from the upper and left angle of the right ventricle, from which the pulmonary artery arises.A tendinous band, which may be named the tendon of the conus arteriosus, extends upward from the right atrioventricular fibrous ring and connects the posterior surface of the conus arteriosus to the aorta. This is also called the infundibulum, and it is the entrance from the right ventricle into the pulmonary artery and pulmonary trunk. The wall of the infundibulum is smooth.

Septomarginal Trabecula

Septomarginal trabecula (or moderator band)

is a muscular band of heart tissue found in the right ventricle. It is well-marked in sheep and some other animals, and frequently extends from the base of the anterior papillary muscle to the ventricular septum.

From its attachments it was thought to prevent overdistension of the ventricle, and was named the "moderator band". However, more recent research has indicated that it is more properly considered part of the electrical conduction system of the heart, and in that capacity it is called the "septomarginal trabecula". The TA name is "trabecula septomarginalis".

The moderator band is often used by radiologists to more easily identify the right ventricle in prenatal ultrasound.

Pulmonary ValvePulmonary Valve

is the semilunar valve of the heart that lies between the right ventricle and the pulmonary artery and has three cusps. Similar to the aortic valve, the pulmonic valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. At the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonic valve.

Pulmonary Valve

Pulmonary Artery

Pulmonary Circulation

Pulmonary ArteryPulmonary arteries carry

blood from the heart to the lungs. They are the only arteries (other than umbilical arteries in the fetus) that carry deoxygenated blood.

In the human heart, the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle. It is short and wide - approximately 5 cm (2 inches) in length and 3 cm (1.2 inches) in diameter. It then branches into two pulmonary arteries (left and right), which deliver deoxygenated blood to the corresponding lung.

Pulmonary Circulation

Pulmonary Circulation is the portion of the cardiovascular system which carries oxygen-depleted blood away from the heart, to the lungs, and returns oxygenated blood back to the heart. The term is contrasted with systemic circulation.

Oxygen-depleted blood from the body leaves the right heart through the pulmonary arteries, which carry it to the lungs, where red blood cells release carbon dioxide and pick up oxygen during respiration. The oxygenated blood then leaves the lungs through the pulmonary veins, which return it to the left heart, completing the pulmonary cycle. The blood is then distributed to the body through the systemic circulation before returning again to the pulmonary circulation.

Left heart is a term used to refer collectively to the left atrium and lef ventricle of the heart; occasionally, this term is intended to reference the left atrium, left ventricle, and the aorta collectively.

The left atrium receives oxygenated pulmonic blood from the pulmonary veins. The blood is then pumped through the mitral valve into the left ventricle, which in turn pumps the blood through the aortic valve into the aorta.

The left side of the heart is thicker than the right because of the requirement to pump blood from the left throughout the body, as opposed to the right side pumping only through the lungs.

Pulmonary veins Left atrium

Left Auricular AppendixMitral valveLeft ventricleAortic valve

Aortic sinusAorta Systemic circulation

Pulmonary Veins

The pulmonary veins carry oxygen-rich blood from the lungs to the left atrium of the heart. They are the only veins in the post-fetal human body that carry oxygenated (red) blood.

• The pulmonary veins return the oxygenated blood from the lungs to the left atrium of the heart. They are four in number, two from each lung, and are destitute of valves. They are

• Right Inferior • Right Superior • Left Inferior • Left Superior

Left AtriumLeft atrium

is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle.

Blood is pumped through the left atrioventricular orifice, which contains the mitral valve. A normal left atrium may be up to 5.5cm in maximum diameter; any larger than this is a sign of cardiac failure. This may occur in cases of mitral regurgitation.

Left Auricular AppendixLeft Auricular Appendix

(left auricula, left auricle)

is a conical muscular pouch connected to the left atrium of the heart. It is somewhat constricted at its junction with the principal cavity; it is longer, narrower, and more curved than the right auricular appendix, and its margins are more deeply indented.

It is directed forward and toward the right and overlaps the root of the pulmonary artery.

Mitral ValveMitral valve (also known

as the bicuspid valve or left atrioventricular valve)

is a dual flap (bi = 2) valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). In Latin, the term mitral means shaped like a miter, or bishop's cap. The mitral valve and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart and control flow.

Left ventricleThe left ventricle

is one of four chambers (two atria and two ventricles) in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.

The left ventricle is longer and more conical in shape than the right, and on transverse section its concavity presents an oval or nearly circular outline. It forms a small part of the sternocostal surface and a considerable part of the diaphragmatic surface of the heart; it also forms the apex of the heart.

Aortic ValveAortic valve

is one of the valves of the heart. It lies between the left ventricle and the aorta.

MorphologyThe aortic valve has

three cusps. These cusps are half moon shaped hence also called aortic semilunar valve. Each cusp has a small swelling in the center called the nodule. Dilatation of the wall of the aorta behind these cusps is called aortic sinus. When the aortic valve is open, the normal size of the orifice is 3-4 cm² in adults.

Aortic Sinus

An aortic sinus is one of the anatomic dilations of the ascending aorta, which occurs just above the aortic valve.

There are generally three aortic sinuses, the left, the right and the posterior.

• The left aortic sinus gives rise to the left coronary artery. • The right aortic sinus gives rise to the right coronary artery. • Usually, no vessels arise from the posterior aortic sinus, which

is therefore known as the non-coronary sinus.

AortaThe aorta (generally

pronounced [eɪˈɔːtə] or "ay-orta") is the largest artery in the human body, originating from the left ventricle of the heart and bringing oxygenated blood to all parts of the body in the systemic circulation.

The course of the AortaThe aorta is usually divided

into five segments/sections:

• Ascending aorta • Arch of aorta • Descending aorta • Thoracic aorta• Abdominal aorta

Ascending aorta, Arch of aorta, Descending aorta

• Ascending Aorta — the section between the heart and the arch of aorta

• Arch of Aorta — the peak part that looks somewhat like an inverted "U"

• Descending Aorta — the section from the arch of aorta to the point where it divides into the common iliac arteries

Thoracic aortaThoracic aorta

is contained in the posterior mediastinal cavity.

It begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth at the aortic hiatus in the diaphragm.

At its commencement, it is situated on the left of the vertebral column; it approaches the median line as it descends; and, at its termination, lies directly in front of the column.

Abdominal AortaAbdominal Aorta

is a large artery in the abdominal cavity. As part of the aorta, it is a direct continuation of descending aorta (of the thorax).

Systemic CirculationSystemic Circulation

is the portion of the cardiovascular system which carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart. The term is contrasted with pulmonary circulation.

Oxygenated blood from the lungs leaves the left heart through the aorta, from where it is distributed to the body's organs and tissues, which absorb the oxygen, through a complex network of arteries, arterioles, and capillaries. The deoxygenated blood is then collected by venules, from where it flows first into veins, and then into the inferior and superior venae cavae, which return it to the right heart, completing the systemic cycle. The blood is then re-oxygenated through the pulmonary circulation before returning again to the systemic circulation.

Layers of the Heart1.) Pericardium

1.1.)Sinusa.) Oblique Sinusb.) Transverse Sinus

2.) Epicardium 3.) Myocardium4.) Endocardium5.) Cardiac skeleton

5.1.) Fibrous trigone 5.2.) Fibrous rings

Pericardium is a double-walled sac that contains the heart and the roots of the

great vessels.

Layers of PericardiumA.) Fibrous Pericardium

is the most superficial layer. It is a dense connective tissue, protecting the heart, anchoring it to the surrounding walls, and preventing it from overfilling with blood. It is continuous with the outer adventitial layer of the neighboring great blood vessels.

B.) Serous Pericardium is deep to the fibrous pericardium. It contains two layers, both

of which function in lubricating the heart to prevent friction from occurring during heart activity.

Pericardial Sinuses

The cul-de-sac enclosed between the limbs of the inverted U of the venous mesocardium lies behind the left atrium and is known as the Oblique Sinus.

The passage between the venous and arterial mesocardia—i.e., between the aorta and pulmonary artery in front and the atria behind—is termed the Transverse Sinus.

Epicardium

describes the outer layer of heart tissue (from Greek; epi- outer, cardium heart). When considered as a part of the pericardium, it is the inner layer, or visceral pericardium.

Its largest constituent is connective tissue and functions as a protective layer. The visceral pericardium apparently produces the pericardial fluid, which lubricates motion between the inner and outer layers of the pericardium.

During ventricular contraction, the wave of depolarization moves from endocardial to epicardial surface.

Myocardium

is the muscular tissue of the heart.

Relationship to other layersThe other tissues of the heart are:

The Endocardium (inner lining, effectively a specialised endothelium) The Epicardium (a connective tissue layer around the heart with a serous surface. It may be considered as the inner (visceral) layer of the pericardium).

CompositionThe myocardium is composed of specialized cardiac muscle cells with an ability not possessed by muscle tissue elsewhere in the body. Cardiac muscle, like other muscles, can contract, but it can also conduct electricity, like nerves.

The blood supply of the myocardium is by the coronary arteries.

Endocardium In the heart, the endocardium is the innermost layer of tissue that

lines the chambers of the heart. Its cells, embryologically and biologically, are similar to the endothelial cells that line blood vessels.

The endocardium overlies the much more voluminous myocardium, the muscular tissue responsible for the contraction of the heart. The outer layer of the heart is termed epicardium and the heart is surrounded by a small amount of fluid enclosed by a fibrous sac called the pericardium.

FunctionRecently, it has become evident that the endocardium, which is

primarily made up of endothelial cells, controls myocardial function. This modulating role is separate from the homeometric and heterometric regulatory mechanisms that control myocardial contractility. Moreover, the endothelium of the myocardial (heart muscle) capillaries, which is also closely appositioned to the cardiomyocytes (heart muscle cells) are involved in this modulatory role. Thus, the cardiac endothelium (both the endocardial endothelium and the endothelium of the myocardial capillaries) controls the development of the heart in the embryo as well as in the adult, for example during hypertrophy. Additionally, the contractility and electrophysiological environment of the cardiomyocyte are regulated by the cardiac endothelium.

The endocardial endothelium may also act as a kind of blood-heart barrier (analogous to the blood-brain barrier), thus controlling the ionic composition of the extracellular fluid in which the cardiomyocytes bathe.

Cardiac skeleton Cardiac skeleton (sometimes called "fibrous skeleton of the heart") refers to

the structure of dense connective tissue in the heart that separates the atria from the ventricles.It is not a "true" skeleton, but it does provide structure and support for the heart, as well as isolating the electric charges that go through the heart.

The left atrioventricular ring is closely connected, by its right margin, with the aortic arterial ring; between these and the right atrioventricular ring is a triangular mass of fibrous tissue, the fibrous trigone, which represents the os cordis seen in the heart of some of the larger animals, as the ox and elephant.

The right and left fibrous rings of heart (anulus fibrosus cordis) surround the atrioventricular and arterial orifices, and are stronger upon the left than on the right side of the heart. The right fibrous ring is known as the anulus fibrosus dexter cordis, and the left is known as the anulus fibrosus sinister

cordis

Heart StructuresA.) Atria

*Interatrial septum*Musculi pectinati

B.) Ventricle

*Interventricular Septum *Trabeculae Carneae *Chordae Tendinae  

*Papillary Muscle

C.) Valve

1.) Atrioventricular valves 1.1.) Mitral valve 1.2.) Tricuspid valve

2.) Semilunar valves 2.1.) Aortic valve 2.2.) Pulmonic valve

Interatrial septumInteratrial Septum is the wall of tissue that separates the

right and left atria of the heart.

Musculi Pectinati

In the right atrium, behind the crest the internal surface of the atrium is smooth, while in front of it the muscular fibers of the wall are raised into parallel ridges resembling the teeth of a comb, and hence named the musculi pectinati (pectinate muscles).

Interventricular Septum

Interventricular SeptumInterventricular septum

(or ventricular septum, or during development septum inferius) is the stout wall separating the lower chambers (the ventricles) of the heart from one another.

The ventricular septum is directed obliquely backward and to the right, and is curved with the convexity toward the right ventricle: its margins correspond with the anterior and posterior longitudinal sulci.

Portions

The greater portion of it is thick and muscular and constitutes the muscular ventricular septum.

Its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum (septum membranaceum).

Trabeculae CarneaeThe trabeculae carneae (columnae carneae) are

rounded or irregular muscular columns which project from the whole of the inner surface of the ventricle, with the exception of the conus arteriosus.

They are of three kinds:1.) Some are attached along their entire length on one side and merely

form prominent ridges,

2.) Others are fixed at their extremities but free in the middle,

3.) While a third set (musculi papillares) are continuous by their bases with the wall of the ventricle, while their apices give origin to the chordæ tendineæ which pass to be attached to the segments of the tricuspid valve.

Chordae TendinaeThe chordae tendineae, or heart strings, are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart.

When the right ventricle of the heart contracts, the blood pressure pushes the tricuspid valve which closes and prevents a backflow of blood into the right atrium. The chordae tendineae prevents the flaps from being everted into the right atrium. Similarly, these cord-like tendons hold in position other flaps like the bicuspid or mitral valve.

Papillary Muscle

Papillary muscles of the heart serve to limit the movements of the mitral and tricuspid valves. These muscles contract to tighten the chordae tendineae, which in turn prevent inversion. This occurs in response to pressure gradients. Instead they brace the valves against the high pressure, preventing regurgitation of ventricular blood back into the atrial cavities.

Heart Valves

Heart valves are valves in the heart that maintain the unidirectional flow of blood by opening and closing depending on the difference in pressure on each side. The mechanical equivalent of the heart valves would be the reed valves.

Mitral ValveThe mitral valve

(also known as the bicuspid valve or left atrioventricular valve), is a dual flap (bi = 2) valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). In Latin, the term mitral means shaped like a miter, or bishop's cap. The mitral valve and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart and control flow.

Tricuspid Valve

The tricuspid valve is on the right side of the heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles. Tricuspid valves may also occur with two or four leaflets, and the number may change during life.

Aortic Valve

Aortic ValveThe aortic valve is one of the valves of the heart. It lies between

the left ventricle and the aorta.

MorphologyThe aortic valve has three cusps. These cusps are half moon

shaped hence also called aortic semilunar valve. Each cusp has a small swelling in the center called the nodule. Dilatation of the wall of the aorta behind these cusps is called aortic sinus. When the aortic valve is open, the normal size of the orifice is 3-4 cm² in adults.

Function & PhysiologyDuring ventricular systole, pressure rises in the left ventricle. When

the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound (S2).

Pumonary Valve

Pumonary Valveis the semilunar valve of the heart that lies between

the right ventricle and the pulmonary artery and has three cusps. Similar to the aortic valve, the pulmonic valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. At the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonic valve.

The closure of the pulmonic valve contributes the P2 component of the second heart sound (S2). The right heart is a low-pressure system, so the P2 component of the second heart sound is usually softer than the A2 component of the second heart sound. However, it is physiologically normal in some young people to hear both components separated during inhalation.

Regions of The Heart1.) Base2.) Apex3.) Grooves

a.) Coronary/atrioventricularb.) Interatrialc.) Anterior interventriculad.) Posterior interventricular 

4.) Surfaces a.) Sternocostal b.) Diaphragmatic

5.) Borders a.) Rightb.) Left

Base of the HeartBase of the heart, directed upward, backward,

and to the right, is separated from the fifth, sixth, seventh, and eighth thoracic vertebræ by the esophagus, aorta, and thoracic duct.

It is formed mainly by the left atrium, and, to a small extent, by the back part of the right atrium.

Somewhat quadrilateral in form, it is in relation above with the bifurcation of the pulmonary artery, and is bounded below by the posterior part of the coronary sulcus, containing the coronary sinus.

On the right it is limited by the sulcus terminalis of the right atrium, and on the left by the ligament of the left vena cava and the oblique vein of the left atrium.

The four pulmonary veins, two on either side, open into the left atrium, while the superior vena cava opens into the upper, and the anterior vena cava into the lower, part of the right atrium.

Apex of the HeartApex of the heart

is the lowest superficial part of the heart.

It is directed downward, forward, and to the left, and is overlapped by the left lung and pleura.

External AnatomyIt lies behind the fifth left

intercostal space, 8 to 9 cm. from the mid-sternal line, slightly medial to the midclavicular line.

Alternately, it can be found about 4 cm. below and 2 mm. to the medial side of the left mammary papilla.

It's function is to pump blood to left atruim

Grooves

Coronary/atrioventricular

Interatrial

Anterior interventricula

Posterior interventricular

Coronary Sulcus

The atria of the heart are separated from the ventricles by the coronary sulcus (coronary groove, auriculoventricular groove, atrioventricular groove); this contains the trunks of the nutrient vessels of the heart, and is deficient in front, where it is crossed by the root of the pulmonary artery.

Interatrial Groove

Interatrial groove, separating the two atria, is scarcely marked on the posterior surface, while anteriorly it is hidden by the pulmonary artery and aorta.

Anterior Interventricular Sulcus

The ventricles of the heart are separated by two grooves, one of which, the anterior longitudinal sulcus (or anterior interventricular sulcus), is situated on the sternocostal surface of the heart, close to its left margin. The other groove separating the ventricles is the posterior interventricular sulcus.

Posterior Interventricular Sulcus

The ventricles are separated by two grooves, one of which, the anterior longitudinal sulcus, is situated on the sternocostal surface of the heart, close to its left margin, the other posterior longitudinal sulcus (posterior interventricular sulcus, inferior interventricular groove), on the diaphragmatic surface near the right margin.

In it run the posterior interventricular artery and middle cardiac vein.

Surfaces

Sternocostal

Diaphragmatic 

Sternocostal Surface of HeartThe sternocostal surface of the heart

(anterior surface of the heart) is directed forward, upward, and to the left.

Its lower part is convex, formed chiefly by the right ventricle, and traversed near its left margin by the anterior longitudinal sulcus.

Its upper part is separated from the lower by the coronary sulcus, and is formed by the atria; it presents a deep concavity, occupied by the ascending aorta and the pulmonary artery.

Diaphragmatic Surface of Heart

The diaphragmatic surface of the heart, directed downward and slightly backward, is formed by the ventricles, and rests upon the central tendon and a small part of the left muscular portion of the diaphragm.

It is separated from the base by the posterior part of the coronary sulcus, and is traversed obliquely by the posterior longitudinal sulcus.

Borders

Right Border of Heart

Left Margin of Heart

Right Border of HeartRight margin of the heart (right border of

heart) is long, and is formed by the right atrium above and

the right ventricle below.

The atrial portion is rounded and almost vertical; it is situated behind the third, fourth, and fifth right costal cartilages about 1.25 cm. from the margin of the sternum.

The ventricular portion, thin and sharp, is named the acute margin; it is nearly horizontal, and extends from the sternal end of the sixth right coastal cartilage to the apex of the heart.

Left Margin of HeartThe left margin of heart (or obtuse margin) is shorter

than the right border of heart, full, and rounded: it is formed mainly by the left ventricle, but to a slight extent, above, by the left atrium.

It extends from a point in the second left intercostal space, about 2.5 mm. from the sternal margin, obliquely downward, with a convexity to the left, to the apex of the heart.

Electrical conduction system of the heart

The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to (and stimulate) the myocardium (Cardiac muscle). After myocardium is stimulated, it contracts. It is the ordered stimulation of the myocardium that allows efficient contraction of the heart, thereby allowing blood to be pumped throughout the body.

Cardiac PacemakerSA nodeAV node

Bundle of HisPurkinje Fibers

Cardiac Pacemaker

The contractions of the heart are controlled by chemical impulses, which fire at a rate which controls the beat of the heart.

The cells that create these rhythmical impulses are called pacemaker cells, and they directly control the heart rate. Artificial devices also called pacemakers can be used after damage to the body's intrinsic conduction system to produce these impulses synthetically.

Sinoatrial node

Sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker) tissue located in the right atrium of the heart. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. These cells are modified cardiac myocytes. They possess some contractile filaments, though they do not contract.

Atrioventricular nodeAtrioventricular node (abbreviated AV

node) is an area of specialized tissue between the atria and the ventricles of the heart, which conducts the normal electrical impulse from the atria to the ventricles. The AV node is also known as the Aschoff-Tawara node.

The AV node receives two inputs from the atria: posteriorly via the crista terminalis, and anteriorly via the interatrial septum.

An important property that is unique to the AV node is decremental conduction. This is the property of the AV node that prevents rapid conduction to the ventricle in cases of rapid atrial rhythms, such as atrial fibrillation or atrial flutter.

Bundle of His

Bundle of His is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node (located between the atria and the ventricles) to the point of the apex of the fascicular branches. The fascicular branches then lead to the Purkinje fibers which innervate the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval. These specialized muscle fibres in the heart were named after the Swiss cardiologist Wilhelm His, Jr., who discovered them in 1893.

Purkinje FibersPurkinje fibers (or Purkyne tissue) are located in the

inner ventricular walls of the heart, just beneath the endocardium. These fibers are specialized myocardial fibers that conduct an electrical stimulus or impulse that enables the heart to contract in a coordinated fashion.

FunctionPurkinje fibers work with the sinoatrial node (SA

node) and the atrioventricular node (AV node) to control the heart rate.

During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from the left and right bundle branches to the myocardium of the ventricles. This causes the muscle tissue of the ventricles to contract and force blood out of the heart — either to the pulmonary circulation (from the right ventricle) or to the systemic circulation (from the left ventricle).

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