The Base of the Heart
The base is located posteriorly and is formed mainly by the left atrium.
It lies opposite T5 to T8 (supine position) and T6 to T9 vertebrae (erect position) and faces superiorly, posteriorly and towards the right shoulder.
The base or posterior aspect of the heart is quadrilateral in shape and it is from its most superior part from which the ascending aorta and pulmonary trunk emerge, and into which the superior vena cava enters.
The base is separated from the diaphragmatic surface of the heart by the posterior part of the coronary groove (L. sulcus).
The heart does not rest on its base. The term refers to the somewhat conical shape of the heart with the base being opposite the apex.