Pericardium The pericardium is a fibroserous sac surrounding the heart and the roots of the great vessels. It consists of two components, 1) the fibrous pericardium and 2) the serous pericardium. The fibrous pericardium is a tough connective tissue outer layer that defines the boundaries of the middle mediastinum. The serous pericardium is thin and consists of two parts: 1) The parietal layer lines the inner surface of the fibrous. 2) The visceral layer adheres to the heart and forms its outer covering. The parietal and visceral layers of serous pericardium are continuous at the roots of the great vessels. The narrow space created between the two layers of serous pericardium, containing a small amount of fluid, is the pericardial cavity. This is pictured in the diagram above as a fist in a filled balloon. This potential space allows for the relatively uninhibited movement of the heart. Fibrous pericardium The fibrous pericardium is a cone-shape