Heart

Cardiac orientation

The general shape and orientation of the heart are that of a pyramid that has fallen over and is resting on one of its sides . Placed in the thoracic cavity, the apex of this pyramid projects forward, downward, and to the left, whereas the base is opposite the apex and faces in a posterior direction (Fig. 1) . The sides of the pyramid consist of:

• diaphragmatic (inferior) surface on which the pyramid rests,
• an anterior (sternocostal) surface oriented anteriorly,
• a right pulmonary surface, and
• a left pulmonary surface.

Fig. 1 Base of the Heart

Because the great veins enter the base of the heart, with the pulmonary veins entering the right and left sides of the left atrium and the superior and inferior venae cavae at the upper and lower ends of the right atrium, the base of the heart is fixed posteriorly to the pericardia! wall, opposite the bodies of vertebrae TV to TVIII (TVI to TIX when standing) . The esophagus lies immediately posterior to the base.

From the base the heart proj ects forward, downward, and to the left, ending in the apex. The apex of the heart is formed by the inferolateral part of the left ventricle (Fig. 2) and is positioned deep to the left fifth intercostal space, 8-9 em from the midsternal line.

Fig. 2 Anterior Surface of the Heart

Surfaces of the heart

The anterior surface faces anteriorly and consists mostly of the right ventricle, with some of the right

atrium on the right and some of the left ventricle on the left (Fig. 2 ).

The heart in the anatomical position rests o n the diaphragmatic surface, which consists of the left ventricle

and a small portion of the right ventricle separated by the posterior interventricular groove (Fig. 3) . This surface faces inferiorly, rests on the diaphragm, is separated from the base of the heart by the coronary sinus, and extends from the base to the apex of the heart.

The left pulmonary surface faces the left lung, is broad and convex, and consists of the left ventricle and a

portion of the left atrium (Fig. 3).

The right pulmonary surface faces the right lung, is broad and convex, and consists of the right atrium

(Fig. 3).

Figs. 3 Diaphragmatic surface of the Heart 

Margins and Borders

Some general descriptions of cardiac orientation refer to right, left, inferior (acute), and obtuse margins:

• The right and left margins are the same as the right and left pulmonary surfaces of the heart.
• The inferior margin is defined as the sharp edge between the anterior and diaphragmatic surfaces of the heart (Figs. 2)-it is formed mostly by the right ventricle and a small portion of the left ventricle near the apex.
• The obtuse margin separates the anterior and left pulmonary surfaces (Fig. 2)-it is round and extends from the left auricle to the cardiac apex (Fig. 2) , and is formed mostly by the left ventricle and superiorly by a small portion of the left auricle.

External sulci

Internal partitions divide the heart into four chambers (i.e. , two atria and two ventricles) and produce surface or external grooves referred to as sulci.

• The coronary sulcus circles the heart, separating the atria from the ventricles {Fig. 4) . As it circles the heart, it contains the right coronary artery, the small cardiac vein, the coronary sinus, and the circumflex branch of the left coronary artery.
• The anterior and posterior interventricular sulci separate the two ventricles-the anterior interventricular sulcus is on the anterior surface of the heart and contains the anterior interventricular artery and the great cardiac vein, and the posterior interventricular sulcus is on the diaphragmatic surface of the heart and contains the posterior interventricular artery and the middle cardiac vein.

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