The heart lies obliquely in the thorax, with the long axis towards the apex. It undergoes rotation during development, so the right sided chambers are mainly anterior, and the atria are mainly to the right of the ventricles.

The posterior surface or base of the heart is formed by the left atrium and the four pulmonary veins.

The left ventricle extends from the interventricular groove to the apex of the heart and forms the lateral border of the heart, and most of the inferior and parts of the lateral and anterior surfaces of the heart.

The right ventricle forms the inferior border of the heart, most of the anterior surface of the heart and one third of the inferior surface.

The right border of the heart is formed by the right atrium and the vena cava.