Pericardiocentesis is an invasive procedure in which the physician removes (aspirates) fluid from the pericardium – a protective fluid-filled sac surrounding the heart. The pericardium is designed to hold a small amount of fluid between its tissue layers, which helps it to cushion, insulate and protect the heart.

In general, physicians recognize two kinds of compressive syndromes that can affect the pericardium and restrict the movement of the heart. The first is constrictive pericarditis, which occurs when the pericardium loses elasticity and becomes thicker and possibly scarred. The second is cardiac tamponade. This occurs when the pericardium fills with excess fluid, thus putting additional pressure on the heart. In addition, these two conditions can occur together. Any number of conditions might cause either constrictive pericarditis or tamponade, including trauma, heart attack, aortic dissection, infection, cancer, or various diseases. If the cause is unknown, it is listed as idiopathic.

Whatever the cause, when fluid begins to build up in the pericardium, the heart's ability to fully fill with blood is reduced due to a limited range of motion. This has a number of effects. First, blood pressure is elevated in the lungs (pulmonary hypertension) because the heart cannot fully expand. In more severe cases, the right side of the heart will be placed under considerable pressure as oxygen-poor blood flows into it. As a result, the muscular wall that separates the right and left sides of the heart (septum) bulges to the left, partially impairing the heart's main pumping chamber, or left ventricle.

Pericardiocentesis is generally reserved for dangerous, acute cases of tamponade. In these instances, it is a life-saving procedure that results in rapid improvement of symptoms. It may also be recommended for patients with subacute tamponade who are beginning to experience symptoms due to fluid accumulation.

The severity of tamponade is related to the filling rate, or the rate at which liquid is pouring into the thin space between the pericardium and the heart muscle. If the problem is acute, it can result in symptoms such as chest pain and difficult breathing. This condition must be treated immediately and is considered a true medical emergency. If the filling rate is slower, it may be known as subacute tamponade and may not have symptoms early on. Later, symptoms are similar to acute tamponade.

Pericardiocentesis has also been used as a diagnostic test, in which a sample of fluid is obtained and analyzed for the presence of viral or bacterial infection or cancer. This test is used most commonly for cases of pericarditis where infection or cancer is suspected. However, its use as a test is somewhat controversial, primarily due to its expense and relatively high risk of complications. Fortunately, the use of fluoroscopy or echocardiogram to help monitor the process is of great help to physicians and has improved both the safety and effectiveness of the procedure. In addition, it can be invaluable for diagnosing or ruling out many forms of pericarditis.

Because of its risk profile, certain patients should not undergo pericardiocentesis. These include patients with aortic dissection. Emergency surgical intervention is warranted in this case.