The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.

There are two layers to the pericardial sac: the fibrous pericardium and the serous pericardium. The serous pericardium, in turn, is divided into two layers, the parietal pericardium, which is fused to and inseparable from the fibrous pericardium, and the visceral pericardium, which is in fact the epicardium, or the outer surface of the heart.

In between the parietal and visceral pericardial layers there is a potential space called the pericardial cavity. It is normally lubricated by a film of pericardial fluid. Too much fluid in the cavity (such as in a pericardial effusion) can result in pericardial tamponade, which refers to compression of the heart within the pericardial sac.

There are two small chambers or sinuses are located where the visceral and parietal pericardia are continuous with one another within the pericardial cavity.

The pericardial sinuses are:

• Oblique pericardial sinus
• Transverse pericardial sinus

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• Pericarditis is an inflammatory condition of the pericardium.
• Pericardial effusion is fluid accumulation in the pericardial sac.
• Constrictive pericarditis occurs when there is a scar encasing the heart that chronically constricts the filling of the heart.
• Cardiac tamponade is a medical emergency in which fluid in the pericardial sac acutely restricts the filling of the heart. This requires surgical drainage or pericardiocentesis.

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