Gross Anatomy of the heart

Heart
The heart is a hollow muscular organ that is somewhat pyramid
shaped and lies within the pericardium in the mediastinum
(Figs. 3.33 and 3.34). It is connected at its base to
the great blood vessels but otherwise lies free within the
pericardium.
Surfaces of the Heart
The heart has three surfaces: sternocostal (anterior), diaphragmatic
(inferior), and a base (posterior). It also has an
apex, which is directed downward, forward, and to the left.
The sternocostal surface is formed mainly by the
right atrium and the right ventricle, which are separated
from each other by the vertical atrioventricular groove
(Fig. 3.34). The right border is formed by the right atrium;
the left border, by the left ventricle and part of the left auricle.
The right ventricle is separated from the left ventricle
by the anterior interventricular groove.
The diaphragmatic surface of the heart is formed
mainly by the right and left ventricles separated by the posterior
interventricular groove. The inferior surface of the
right atrium, into which the inferior vena cava opens, also
forms part of this surface.
The base of the heart, or the posterior surface, is formed
mainly by the left atrium, into which open the four pulmonary
veins (Fig. 3.35). The base of the heart lies opposite the apex.
The apex of the heart, formed by the left ventricle, is
directed downward, forward, and to the left (Fig. 3.34).
It lies at the level of the fifth left intercostal space, 3.5 in.
(9 cm) from the midline. In the region of the apex, the apex
beat can usually be seen and palpated in the living patient.