The heart is enclosed in a membranous sac called the pericardium. It has two layers- the fibrous pericardium which is the outer layer and the serous pericardium that lies inside the fibrous pericardium. The serous pericardium has two layers - the outer parietal and the inner visceral layer. The parietal layer lines the fibrous pericardium and the visceral layer the surfaces of the heart. This visceral layer is also called the epicardium.