ANATOMY OF HEARTPrepared by: Sharmin Susiwala

Front view of heart and lungs.

The Heart(Cor)

• The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium.

• It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane.

Size.—o The heart, in the adult, measures about - 12 cm. in length, - 8 to 9 cm. in breadth at the broadest part, - 6 cm. in thickness. o Its weight, in the male, varies from 280 to 340 grams; in the female,

from 230 to 280 grams.

Component Parts.— “gross anatomy of the heart”• The heart is subdivided by septa into right and left halves, and a

constriction subdivides each half of the organ into two cavities, - the upper cavity being called the atrium, - the lower the ventricle.• The heart therefore consists of four chambers, viz., right and left

atria, and right and left ventricles.• The division of the heart into four cavities is indicated on its surface

by grooves. • The atria are separated from the ventricles by the coronary

sulcus (auriculoventricular groove)• The interatrial groove, separating the two atria• The ventricles are separated by two grooves, one of which is,

the anterior longitudinal sulcus, the other posterior longitudinal sulcus.

Base (basis cordis):- Directed upward, backward, and to the right, is separated from the fifth, sixth,

seventh, and eighth thoracic vertebrae 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.

Apex (apex cordis):- The apex is directed downward, forward, and to the left, and is overlapped by the

left lung and pleura- It lies behind the fifth left intercostal space, 8 to 9 cm. from the mid-sternal line, or

about 4 cm. below and 2 mm. to the medisial side of the left mammary papilla.

Sternocostal surface: - 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: - 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.

Right margin of the heart: - Is long- Is formed by the right atrium above and the right ventricle below.

Left or obtuse margin of the heart: - Is shorter, full, and rounded - It is formed mainly by the left ventricle, but to a slight extent, above,

by the left atrium.

• Structure.— The heart consists of muscular fibers, and of fibrous rings

which serve for their attachment. It is covered by the visceral layer of the serous pericardium

(epicardium), and lined by the endocardium. Between these two membranes is the muscular wall

or myocardium.

Cardiac Muscular Tissue

CHAMBERS OF THE HEARTRight Atrium (atrium dextrum; right auricle).—

The right atrium is larger than the left, but its walls are somewhat thinner, measuring about 2 mm.

It consists of two parts: a principal cavity, or sinus venarum, situated posteriorly, and an anterior, smaller portion, the auricula.

Sinus Venarum (sinus venosus).—- The sinus venarum is the large quadrangular cavity placed between the two venæ cavæ. - Its walls, which are extremely thin, are connected below with the right ventricle, and medially with the

left atrium, but are free in the rest of their extent.

Auricula (auricula dextra; right auricular appendix).—- The auricula is a small conical muscular pouch, the margins of which 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.

• The separation of the auricula from the sinus venarum is indicated externally by a groove, the terminal sulcus, which extends from the front of the superior vena cava to the front of the inferior vena cava.

• On the inner wall of the atrium the separation is marked by a vertical, smooth, muscular ridge, the terminal crest. (crista terminalis)

• 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.

• Its interior presents the following parts:1. Openings » Superior vena cava. Inferior vena cava. Coronary sinus. Foramina venarum minimarum. Atrioventricular.

2. Valves »• Valve of the inferior vena cava.• Valve of the coronary sinus.

3. Others » Fossa ovalis. Limbus fossæ ovalis. Intervenous tubercle. Musculi pectinati. Crista terminalis.

1. Openings:• Superior Vena cava- The superior vena cava returns the blood from the upper

half of the body, and opens into the upper and back part of the atrium, the direction of its orifice being downward and forward. Its opening has no valve.

• Inferior Vena cava- The inferior vena cava, larger than the superior, returns the blood from the lower half of the body, and opens into the lowest part of the atrium, near the atrial septum, its orifice being directed upward and backward, and guarded by a rudimentary valve, the valve of the inferior vena cava (Eustachian valve).

• Coronary sinus- The coronary sinus opens into the atrium, between the orifice of the inferior vena cava and the atrioventricular opening. It returns blood from the substance of the heart and is protected by a semicircular valve, the valve of the coronary sinus (valve of Thebesius).

• Foramina Venerum minimum- The foramina venarum minimarum (foramina Thebesii) are the orifices of minute veins (venœ cordis minimœ), which return blood directly from the muscular substance of the heart.

• Atrioventricular Opening- The atrioventricular opening (tricuspid orifice) is the large oval aperture of communication between the atrium and the ventricle; it will be described with the right ventricle.

2. Valves:• Valve of inferior Venacava- The valve of the inferior vena cava (valvula venœ cavœ 

inferioris [Eustachii]; Eustachian valve) is situated in front of the orifice of the inferior vena cava. It is semilunar in form.

     In the fetus this valve is of large size, and serves to direct the blood from the inferior vena cava, through the foramen ovale, into the left atrium.

     In the adult it occasionally persists, and may assist in preventing the reflux of blood into the inferior vena cava; more commonly it is small, and may present a cribriform or filamentous appearance; sometimes it is altogether wanting.

• Valve of coronary sinus- The valve of the coronary sinus (valvula sinus coronarii [Thebesii]; Thebesian valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of the coronary sinus. It prevents the regurgitation of blood into the sinus during the contraction of the atrium. This valve may be double or it may be cribriform.

3. Fossa Ovalis:• The fossa ovalis is an oval depression on the septal wall of the atrium, and

corresponds to the situation of the foramen ovale in the fetus. • It is situated at the lower part of the septum, above and to the left of the orifice

of the inferior vena cava.

4. Limbus Fossa Ovalis:• The limbus fossæ ovalis (annulus ovalis) is the prominent oval margin of the fossa

ovalis.

5. Intervenous Tubercle:• The intervenous tubercle (tuberculum intervenosum; tubercle of Lower) is a

small projection on the posterior wall of the atrium, above the fossa ovalis.

Right Ventricle (ventriculus dexter).—

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

• Its anterosuperior surface is rounded and convex, and forms the larger part of the sternocostal surface of the heart.

• Its under surface is flattened, rests upon the diaphragm, and forms a small part of the diaphragmatic surface of the heart.

• Its posterior wall is formed by the ventricular septum, which bulges into the right ventricle, so that a transverse section of the cavity presents a semilunar outline.

• Its upper and left angle forms a conical pouch, the conus arteriosus, 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.

• The wall of the right ventricle is thinner than that of the left, the proportion between them being as 1 to 3; it is thickest at the base, and gradually becomes thinner toward the apex.

• Its interior presents the following parts:1. Openings »• Right atrioventricular. • Pulmonary artery.

2. Valves » • Tricuspid.• Pulmonary.

3. Others »• Trabeculae carnae.• Chordae tendineae

1. Openings:• Right atrioventricular Orifice- The right atrioventricular orifice is the large oval aperture of communication

between the right atrium and ventricle. Situated at the base of the ventricle, it measures about 4 cm. in diameter and is

surrounded by a fibrous ring, covered by the lining membrane of the heart; it is considerably larger than the corresponding aperture on the left side, being sufficient to admit the ends of four fingers.

It is guarded by the tricuspid valve.• Opening of Pulmonary artery- The opening of the pulmonary artery is circular in form, and situated at the

summit of the conus arteriosus, close to the ventricular septum. It is placed above and to the left of the atrioventricular opening, and is guarded by

the pulmonary semilunar valves.

2. Valves:• Tricuspid valve (valvula tricuspidalis)- consists of three somewhat triangular cusps or segments.

The 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, and a third, the medial or septal cusp, to the ventricular septum.

Their central parts are thick and strong, their marginal portions thin and translucent Their bases are attached to a fibrous ring surrounding the atrioventricular orifice and are also joined

to each other so as to form a continuous annular membrane, while their apices project into the ventricular cavity.

Their atrial surfaces, directed toward the blood current from the atrium, are smooth; their ventricular surfaces, directed toward the wall of the ventricle, are rough and irregular, and, together with the apices and margins of the cusps, give attachment to a number of delicate tendinous cords, the chordae tendineae

The trabeculae carneae (columnœ carneœ) 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: some are attached along their entire length on one side and merely form prominent ridges, others are fixed at their extremities but free in the middle, 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.

There are two papillary muscles, anterior and posterior:- of these, the anterior is the larger, and its chordæ tendineæ are connected with the

anterior and posterior cusps of the valve- the posterior papillary muscle sometimes consists of two or three parts; its chordæ

tendineæ are connected with the posterior and medial cusps. A muscular band frequently extends from the base of the anterior papillary muscle to

the ventricular septum. From its attachments it may assist in preventing over distension of the ventricle, and so has been named the moderator band.

• Pulmonary semilunar valves: Three in number, two in front and one behind. They are attached, by their convex margins, to the wall of the artery, at its junction

with the ventricle, their free borders being directed upward into the lumen of the vessel.

The free and attached margins of each are strengthened by tendinous fibers, and the former presents, at its middle, a thickened nodule (corpus Arantii).

From this nodule tendinous fibers radiate through the segment to its attached margin, but are absent from two narrow crescentic portions, the lunulae, placed one on either side of the nodule immediately adjoining the free margin.

Between the semilunar valves and the wall of the pulmonary artery are three pouches or sinuses (sinuses of Valsalva).

Left Atrium (atrium sinistum; left auricle).—

• The left atrium is rather smaller than the right, but its walls are thicker, measuring about 3 mm.

• It consists, like the right, of two parts, a principal cavity and an auricula. • The principal cavity: is cuboidal in form, and concealed, in front, by the

pulmonary artery and aorta; in front and to the right it is separated from the right atrium by the atrial septum; opening into it on either side are the two pulmonary veins.

• Auricula (auricula sinistra; left auricular appendix).—- The auricula is somewhat constricted at its junction with the principal cavity- It is longer, narrower, and more curved than that of the right side, and its

margins are more deeply indented. - It is directed forward and toward the right and overlaps the root of the

pulmonary artery.

The interior of the left atrium presents the following parts:1. Openings of the four pulmonary veins.2. Left atrioventricular opening.3. Musculi pectinati.

• Opening of pulmonary veins: four in number, open into the upper part of the posterior surface of the left

atrium—two on either side of its middle line: they are not provided with valves. • Left atrioventricular opening: is the aperture between the left atrium and ventricle, and is rather smaller than

the corresponding opening on the right side.• Musculi pectinati: Fewer and smaller than in the right auricula, are confined to the inner surface

of the auricula.

• On the atrial septum may be seen a lunated impression, bounded below by a crescentic ridge, the concavity of which is turned upward. The depression is just above the fossa ovalis of the right atrium.

Left Ventricle (ventriculus sinister).—

• 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. • Its walls are about three times as thick as those of the right ventricle.

• Its interior presents the following parts:

1. Openings »• Left atrioventricular. • Aortic.

2. Valves »• Bicuspid or Mitral.• Aortic.

3. Others »• Trabeculæ carneæ.• Chordæ tendineæ

1. Openings:• Left atrioventricular opening (mitral orifice) : is placed below and to the left of the aortic orifice. It is a little smaller than the corresponding aperture of the opposite side, admitting

only two fingers. It is surrounded by a dense fibrous ring, covered by the lining membrane of the

heart, and is guarded by the bicuspid or mitral valve.• Aortic opening: is a circular aperture, in front and to the right of the atrioventricular, from which it

is separated by the anterior cusp of the bicuspid valve. Its orifice is guarded by the aortic semilunar valves. The portion of the ventricle immediately below the aortic orifice is termed

the aortic vestibule, and possesses fibrous instead of muscular walls.

2. Valves:• Bicuspid or mitral valve (valvula bicuspidalis [metralis]): is attached to the circumference of the left atrioventricular orifice in the same

way that the tricuspid valve is on the opposite side.

It consists of two triangular cusps, formed by duplicatures of the lining membrane, strengthened by fibrous tissue, and containing a few muscular fibers.

The cusps are of unequal size, and are larger, thicker, and stronger than those of the tricuspid valve.

The larger cusp is placed in front and to the right between the atrioventricular and aortic orifices, and is known as the anterior or aortic cusp

The smaller or posterior cusp is placed behind and to the left of the opening. Two smaller cusps are usually found at the angles of junction of the larger. The cusps of the bicuspid valve are furnished with chordæ tendineæ, which are

attached in a manner similar to those on the right side; they are, however, thicker, stronger, and less numerous.

• Aortic semilunar valves: three in number, and surround the orifice of the aorta Two are anterior (right and left) and one posterior. They are similar in structure, and in their mode of attachment, to the pulmonary

semilunar valves, but are larger, thicker, and stronger The lunulæ are more distinct, and the noduli or corpora Arantii thicker and more

prominent. Opposite the valves the aorta presents slight dilatations, the aortic sinuses (sinuses of 

Valsalva), which are larger than those at the origin of the pulmonary artery.

The trabeculæ carneæ are of three kinds, like those upon the right side, but they are more numerous, and present a dense interlacement, especially at the apex, and upon the posterior wall of the ventricle.

The musculi papillares are two in number, one being connected to the anterior, the other to the posterior wall; they are of large size, and end in rounded extremities from which the chordæ tendineæ arise.

The chordæ tendineæ from each papillary muscle are connected to both cusps of the bicuspid valve.

• Vessels—The arteries supplying the heart are the right and left coronary from the aorta; the veins end in the right atrium.

• The lymphatics end in the thoracic and right lymphatic ducts.• The nerves are derived from the cardiac plexus, which are formed partly from the

vagi, and partly from the sympathetic trunks. They are freely distributed both on the surface and in the substance of the heart, the separate nerve filaments being furnished with small ganglia.