The pericardium consists of two layers: the inner visceral layer, which is attached to the epicardium, and an outer parietal layer. About 50 mL of serous fluid is normally present and provides lubrication between the two layers. The pericardial reflection encompasses the heart and great vessels. The pericardium stabilizes the heart in anatomic position and reduces contact between the heart and the surrounding structures. It is composed of fibrous tissue, and although it will permit moderate changes in cardiac size, it cannot stretch rapidly enough to accommodate rapid dilation of the heart or accumulation of fluid without increasing intrapericardial (and, therefore, intracardiac) pressure.
The pericardium is often involved by processes that affect the heart, but it may also be affected by diseases of adjacent tissues and may itself be a primary site of disease.