pericardium membranous sac around the heart , which is of two portions, fibrous pericardium (the outer, tough connective tissue), and serous pericardium (delicate, consists of parietal pericardium, outer layer of the serous membrane, lines inner surface of fibrous pericardium, visceral pericardium (epicardium), the inner layer of the serous membrane, that covers the heart, in which the pericardial cavity space between the visceral and parietal layers separates each one