The external surfaces of the heart are as following:

• Diaphragmatic surface - formed mainly by the left ventricle and right ventricle;
• Anteriorly - sternocostal surface - formed mainly by the right ventricle and right atrium;
• Laterally - pulmonary surfaces:
  • Left pulmonary surface - formed by lateral surface of left ventricle;
  • Right pulmonary (RA) surface - formed by lateral surface of right atrium;
• Posteriorly - base of the heart - formed mainly by the left atrium;
• Apex - formed by the left ventricle.

Base of the heart

The base of the heart is quadrilateral, oriented posteriorly and consists of the left atrium, a small portion of the right atrium, and the proximal parts of the great veins (superior and inferior venae cavae and the pulmonary veins). 

It is fixed posteriorly to the pericardial wall, at the level of the bodies of 5th to 8th thoracic vertebrae (6th to 9th when standing). The esophagus is located immediately posterior to the base of the heart.

Apex of the heart

The apex of the heart is formed by the infero-lateral part of the left ventricle and it is located deep to the left fifth intercostal space, 8 to 9 cm from the midcentral line.

Sternocostal surface

The anterior surface or sternocostal surface of the heart consists mostly of the right ventricle, with part of the right atrium on the right and part of the left ventricle on the left.

Diaphragmatic surface

The heart in its anatomical position rests on the diaphragmatic surface, which faces inferiorly, lies on the diaphragm and consists of the left ventricle and a small part of the right ventricle separated by the posterior interventricular groove. This surface is separated from the base of the heart by the coronary sinus.

Pulmonary surface

The pulmonary surfaces of the heart face the lungs, and these surfaces are broad and convex. The left pulmonary surface consists of the left ventricle and a part of the left atrium, while the right pulmonary surface consists of the right atrium.