The pericardial cavity is the potential space formed between the two layers of serous pericardium around the heart. Normally, it contains a small amount of serous fluid that acts to reduce surface tension and lubricate. Therefore, the cavity facilitates the free movement of the heart.

The cavity surrounds the heart and is continuous with it at all but the points of entry and exit of great vessels. The layers of pericardium form two distinct 'tubes' around groups of these vessels:

• one interconnecting the:
• inferior vena cava
• superior vena cava
• pulmonary veins
• the other connecting the:
• aorta
• pulmonary trunk

It is the disposition of these 'tubes' of pericardium and vessels through the cavity that forms the oblique and transverse sinuses.

Excessive fluid within the pericardial cavity is termed a pericardial effusion. It can lead to cardiac tamponade. Pericardiocentesis may be used to treat, and possibly diagnose the cause of, an effusion.