The conical sac of fibrous tissue that surrounds the heart and the roots of the great blood vessels.

The pericardium's outer coat (the parietal pericardium) is tough and thickened, loosely cloaks the heart, and is attached to the central part of the diaphragm and the back of the breastbone. Its inner coat (the visceral pericardium or epicardium) is double, with one layer closely adherent to the heart and the other lining the inner surface of the outer coat.

The intervening space between these layers is filled with pericardial fluid. This small amount of fluid acts as a lubricant to allow normal heart movement within the chest.

1. Pericardial inflammation with elevations resembling hair.
2. A pericardium coated with a roughened layer of fibrinous exudate (substance that has oozed out the essential portion of a blood clot).

A fibrous and membranous sac which surrounds the heart: The pericardium is composed of two layers, the visceral pericardium, which is closest to the heart; and the parietal ("wall") pericardium, that is lining the outer fibrous coat.

The pericardial cavity, between the visceral pericardium and the parietal pericardium; normally contains 10 to 15 mL (0.33814 to 0.50721 US fluid ounces) of pericardial fluid, which lubricates the membranes while the heart is beating.