What is the Pericardium?

The pericardium is a double-walled sac that contains the heart and the roots of the great vessels. In plain terms the pericardium surrounds the heart and bases of the pulmonary artery and aorta. This membrane is comprised of two layers, an outer layer known as the parietal layer and an inner layer called the epicardium. The outer layer helps to line the whole of the chest cavity, while the inner layer lines the heart.