The pericardium is a double-walled sac that contains the heart and the roots of the great vessels. There are three layers to this sac: the fibrous pericardium, serous pericardium, and the pericardial cavity.
The fibrous pericardium is the most superficial layer. It is a dense connective tissue layer which functions in protecting the heart, anchoring it to the surrounding walls and preventing it from overfilling with blood.
The serous pericardium is deep to the fibrous pericardium. It contains two layers, both of which function in lubricating the heart to prevent friction from occurring during heart activity. The layer next to the fibrous pericardium is the parietal layer, and the layer next to the heart is the visceral layer, also known as the epicardium. Between these two layers exists a small cavity called the pericardial cavity, which contains a supply of serous fluid .
Pericarditis is inflammation of the pericardium. It can cause fluid to build up in the sac. Excessive amounts of fluid may lead to cardiac tamponade by physically blocking the heart from beating properly or compression of the great vessels of the heart.
Traditional Chinese theory
See Pericardium (Zang) for a description of the pericardium according to the Zang Fu theory of Traditional Chinese Medicine.