Cardiac tamponade most commonly results from accumulation of blood or other fluids within the pericardial sac. However, there is a growing body of clinical evidence showing that pneumopericardium can lead to cardiac tamponade in a large number of patients. Including those in the present report, a total of 252 patients with pneumopericardium are available for review. Interestingly, cardiac tamponade developed in 94 patients, or 37% of this group, because of air within the pericardial space. Pneumopericardium resulting in tamponade most frequently occurs in trauma patients or in newborn infants requiring positive pressure ventilation. This syndrome can be recognized promptly because of its characteristic physical findings and radiographic features. Although air tamponade can be treated effectively by either needle aspiration or insertion of a pericardial tube, the development of a pneumopericardium is a bad prognostic sign. Out of the 221 patients reported in the literature whose outcome is known, 127 (57%) died. In the group with a tension pneumopericardium, the mortality was 56% (53 out of 94 patients). Even without the development of tension, however, pneumopericardium was associated with a 58% mortality (74 out of 127 patients) due to other underlying disease processes.