The pericardium, or pericardial sac, is a fibroserous membrane that surrounds the heart from all sides and encloses the roots of the great vessels. The pericardium defines the middle mediastinum, which is the middle compartment of the inferior mediastinum.

The pericardium has several functions - it protects and lubricates the heart to prevent friction during heart contractions. It limits the motions of the heart and keeps it in place within the thorax. Also, it prevents the heart from stretching, excessive dilatations and overfilling with blood. Moreover, the pericardium acts as a mechanical barrier and protects the heart from various harmful factors and pathological agents such as viruses and bacteria.

The pericardium consists of two layers:

Fibrous layer (fibrous pericardium) - the outermost layer;
Serous layer (serous pericardium) - the innermost double layer, consisting of the parietal and visceral sublayers.

Fibrous pericardium

The fibrous pericardium appears as a conical-shaped sac. It is formed by dense irregular connective tissue. Overall, the fibrous pericardium is connected to the surrounding structures with the help of several ligaments.

The inferior aspect of the pericardium is attached to the central tendon of the diaphragm by the pericardiophrenic ligament.

The superior aspect or the apex of the fibrous pericardium fuses with the outer loose connective tissue layer (adventitia) of the great vessels exiting and entering the heart.

Also, ligamentous fibers attach the anterior aspect of the fibrous pericardium to the posterior aspect of the sternum. These fibers form the superior and inferior sternopericardial ligaments.

The superior sternopericardial ligament connects the superior anterior aspect of the pericardium with the posterior aspect of the manubrium of the sternum, while the inferior sternopericardial ligament stretches between the inferior anterior aspect of the pericardium and the posterior aspect of the xiphoid process of the sternum.

Posteriorly, the pericardium is related to the posterior compartment of the inferior mediastinum.

Serous pericardium

As mentioned previously, the serous pericardium is the inner layer that lines the fibrous pericardium. It contains mesothelial cells and consists of two smaller sublayers:

Parietal layer - the outer sublayer that is fused with the inner surface of the fibrous pericardium and is inseparable from it;
Visceral layer (epicardium) - the inner sublayer that directly covers the heart; it also forms the outermost layer of the heart wall.

Pericardial cavity

Between the parietal and visceral sublayers of the serous pericardium is a potential space known as the pericardial cavity. It contains a small amount (0.3 - 1.7 oz or 10 - 50 ml) of a serous fluid known as the pericardial fluid. Its main function is to lubricate both layers and reduce friction between them when the heart contracts.

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Pericardium