A memranaceous cover enveloping the heart. It consists of two parts: the outer, fibrous and more rigid envelope firmly connected to the large vessels coming out from the heart and the serous inner envelope.

The latter has two layers: the inner one, Epicardium (outer heart layer) is adjacent to the heart muscle and the outer one covers the fibrous part from inside.

A small amount of fluid is contained between these two layers, intended to prevent friction between the two surfaces during the excursions of the heart.