The pericardium is a fibrous sac that encloses the heart and great vessels. It keeps the heart in a stable location in the mediastinum, facilitates its movements, and separates it from the lungs and other mediastinal structures. It also supports physiological cardiac function. The pericardium consists of two layers: the fibrous and the serous. The fibrous pericardium is a conical-shaped sac. Its apex is fused with the roots of the great vessels at the base of the heart. Its broad base overlies the central fibrous area of the diaphragm with which it is fused.

Source: NIH