The pericardium is a fibro-serous sac that surrounds the heart and restricts its movement. It has two layers - an outer fibrous layer that maintains the heart's position and an inner serous layer with parietal and visceral layers separated by pericardial fluid. The pericardium protects the heart and provides lubrication as the heart beats within its sac. It has reflections around the major blood vessels leaving the heart and contains openings that allow for blood vessel passage.