Last updated: 02/17/2009

The heart is surrounded by a membrane covering called the pericardial sac. The sac consists of two layers, the parietal (outer) and visceral (inner) layer, and normally contains a small amount of fluid to cushion and lubricate the heart as it contracts...

and expands. When too much fluid gathers in the pericardial cavity, the space between the pericardium and the outer layers of the heart, a condition known as pericardial effusion occurs. Abnormal amounts of fluid may result from:

• pericarditis, infection caused by inflammation of the pericardial sac
• trauma, such as an abnormal collection of blood due to an accident
• surgery or invasive heart procedures
• heart attack (myocardial infarction) or congestive heart failure, which occurs when the heart looses its pumping capability due to a heart condition
• kidney (renal) failure
• cancer (producing malignant effusions)

The rate of pericardial fluid accumulation is important. If fluid accumulation develops slowly, then problems with blood flow will not develop until fluid retention becomes massive. Blood can also enter the pericardial sac (hemopericardium) due to trauma, blood-thinning medications, or disease. When there is rapid or excessive build-up of fluid or blood in the pericardial cavity, the resulting compression on the heart impairs the pumping action of the vascular system (a condition called cardiac tamponade). Pericardiocentesis can be used in such an emergency situation to remove the excess accumulations of blood or fluid from the pericardial sac. For diagnostic purposes, pericardiocentesis may be advised in order to obtain fluid samples from the sac for laboratory analysis.

Prior to the discovery of echocardiography, pericardiocentesis was a risky procedure. The clinician had to insert a long needle below the breastbone into the pericardial sac without internal visualization. This blind approach was associated with damage to the lungs, coronary arteries, myocardium, and liver. However, with direct visualization using echocardiography, pericardiocentesis can now be performed with minor risk. Some risk is still associated with the procedure since it is considered an invasive measure.