Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

The heart lies in a loose-fitting sac called the pericardium. This sac is composed of an outerfibrous portion and an inner serous portion. The inner portion consists of two layers:• The parietal layer lining the inside of the fibrous pericardium• The visceral layer (epicardium) adhering to the exterior surface of the heart.Between the parietal and visceral layers is a potential space, the pericardial space, which containsa few drops of pericardial fluid. This fluid reduces friction during movement of the heart.The walls of the heart are composed of three layers:• The epicardium or outer layer of the heart (the visceral layer of the serous pericardiumdescribed above)° The myocardium or heart muscle• The endocardium or inner lining of the four chambers of the heart.104