Pericardial sac or pericardium is a fibrous tissue that surrounds the heart. It has two coats:
the outter coat-parietal pericardium
the inner coat-visceral pericardium or epicardium which is double-layered and contains pericardial fluid between those two layers (pericardial fluid is necessary as a lubricant for the heart movement).
Besides lubrication, percardium also protects heart from infections, fixes it and limits its movements.
