A tough, double-layered sac known as the pericardium surrounds the heart. The inner layer of the pericardium, known as the epicardium, rests directly on top of the heart muscle. The outer layer of the pericardium attaches to the breastbone and other structures in the chest cavity and helps hold the heart in place. Between the two layers of the pericardium is a thin space filled with a watery fluid that helps prevent these layers from rubbing against each other when the heart beats.

 What is the pericardium?

 The pericardium is the fluid filled sac that surrounds the heart and the proximal ends of the aorta, vena cava and the pulmonary artery.

 Function:

 Keeps the heart contained in the chest cavity.

 Prevents the heart from overexpanding when blood volume increases.

 Limits heart motion.