Pericardiocentesis is the aspiration of fluid from the pericardial space that surrounds the heart. This procedure can be life saving in patients with cardiac tamponade, even when it complicates acute type A aortic dissection and when cardiothoracic surgery is not available. 
Cardiac tamponade is a time sensitive, life-threatening condition that requires prompt diagnosis and management. Historically, the diagnosis of cardiac tamponade has been based on clinical findings. Claude Beck, a cardiovascular surgeon, described 2 triads of clinical findings that he found associated with acute and chronic cardiac tamponade. The first of these triads consisted of hypotension, an increased venous pressure, and a quiet heart. It has come to be recognized as Beck's triad, a collection of findings most commonly produced by acute intrapericardial hemorrhage. Subsequent studies have shown that these classic findings are observed in only a minority of patients with cardiac tamponade. 
The detection of pericardial fluid has been facilitated by the development and continued improvement of echocardiography.  Cardiac ultrasound is now accepted as the criterion standard imaging modality for the assessment of pericardial effusions and the dynamic findings consistent with cardiac tamponade. With echocardiography, the location of the effusion can be identified, the size can be estimated (small, medium, or large), and the hemodynamic effects can be examined by assessing for abnormal septal motion, right atrial or right ventricular inversion, and decreased respiratory variation of the diameter of the inferior vena cava.