Base of the hea is formed mainly by:

The hea 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.The right border is formed by the right atrium; the left border, by the left ventricle and pa of the left auricle.The diaphragmatic surface of the hea is formed mainly by the right and left ventricles. The inferior surface of the right atrium, into which the inferior vena cava opens, also forms pa of this surface.The base of the hea, or the posterior surface, is formed mainly by the left atrium, into which open the four pulmonary veins.