Heart Anatomy

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 midline.

Size

The heart, in the adult, measures about 12cm. in length, 8-9cm. in breadth at the broadest part, and 6cm. in thickness. Its weight, in the male, varies from 280-340g; in the female, from 230-280g. The heart continues to increase in weight and size up to an advanced period of life; this increase is more marked in men than in women.

Parts

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:

* right atrium
* left atrium
* right ventricle
* left ventricle

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 (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. The interatrial groove, separating the two atria, is scarcely marked on the posterior surface, while anteriorly it is hidden by the pulmonary artery and aorta. 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, on the diaphragmatic surface near the right margin; these grooves extend from the base of the ventricular portion to a notch, the incisura apicis cordis, on the acute margin of the heart just to the right of the apex.

Heart valves

The outflow of each chamber is guarded by a heart valve:

* atrioventricular valves
o tricuspid valve
o mitral valve
* aortic valve
* pulmonary valve

Surfaces

The base (basis cordis) 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 (SVC) opens into the upper, and the anterior vena cava into the lower, part of the right atrium.

The apex (apex cordis) 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, 8-9cm. from the mid-sternal line, or about 4cm. below and 2mm. to the medial side of the left mammary papilla.

The sternocostal surface 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. The 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. It is separated from the base by the posterior part of the coronary sulcus, and is traversed obliquely by the posterior longitudinal sulcus. The right margin of the 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 1.25cm. 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 costal cartilage to the apex of the heart.

The left or obtuse margin is shorter, 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 2.5mm. from the sternal margin, obliquely downward, with a convexity to the left, to the apex of the heart.

This article used a transcription from the 20th U.S. edition of Gray's Anatomy of the Human Body, originally published in 1918 and therefore lapsed into the public domain as a seed. Please edit as necessary.

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