The heart is a central organ of the circulatory system, that lies in the middle mediastinum covered by the pericardium

The pericardium is a fibroserous double-walled sac that encloses the heart, the pericardial fluid and the roots of the great vessels, and is situated within the inferior middle mediastinum. 

Its function is to protect and lubricate the moving surfaces of the heart.

Layers of the perdicardium

The pericardium consists of two layers:

• Fibrous layer - outermost layer of the pericardium
• Serous layer - the inner layer of the pericardium.

Fibrous Layer

The fibrous layer of the pericardium consists of dense connective tissue. It is attached to the central tendon of the diaphragm via the pericardiacophrenic ligament whose fibers merge with the tunica adventitia of the vessels which enter and exit the heart. The pericardial sac also attaches via ligamentous fibers to the sternum and due to these attachments it is affected by the movements of the heart, the great vessels, the sternum and the diaphragm.

Serous pericardium

The serous pericardium consists of two layers:

• Parietal layer - fused and inseparable from the fibrous pericardium;
• Visceral layer (a.k.a epicardium) - attached to the outer surface of the heart itself.

Pericardial cavity

The pericardial cavity is a potential space found between the two layers of the serous pericardium. It contains lubricating serous fluid known as pericardial fluid.