The pericardium is the double walled, fluid-filled sac that surrounds the heart and the proximal ends of the great blood vessels. The two layers of the pericardium are the fibrous pericardium and the serous pericardium. The pericardium functions in protecting and lubricating the heart. Inside of the pericardium is the pericardial cavity. This cavity is full of fluid that reduces friction.

Péricarde