Background-Volume expansion has been proposed as an alternative treatment for cardiac tamponade; however, the scientific evidence for this recommendation is very poor. Methods and Results-Forty-nine unselected patients (23 males; age 55Ϯ16 years) with large pericardial effusion and hemodynamic tamponade underwent fluid overload with intravenous administration of 500 mL of normal saline over 10 minutes. Cardiac index and intrapericardial, left ventricular end-diastolic, right atrial, and right ventricular end-diastolic pressures were measured during basal state (tamponade), after fluid overload, and after pericardiocentesis. Twenty-eight patients (57%) had physical signs of tamponade, and 10 (20%) were hypotensive. Size of pericardial effusion was 31Ϯ13 mm. Initial mean arterial pressure was 88Ϯ21 mm Hg, and cardiac index was 2.46Ϯ0.80 L · min Ϫ1 · m