Previous studies have emphasized injury mechanism, wound site, and presenting vital signs as critical determinants for survival following penetrating cardiac injury. Our experience suggests pericardial tamponade is another crucial factor and is the basis for this study. Prognostic features were reviewed in 100 consecutive, unselected patients with acute cardiac injuries. Mechanism was stab wound in 57, and gunshot injury in 43. Location included right ventricle in 55, left ventricle in 49, right atrium in 16, and left atrium in seven. Overall salvage was 31%,; 27 (47%) of 57 stab wounds, four (9%) of 43 gunshot wounds, 22 (49%) of 45 right, and nine (23%) of 39 left heart wounds. The presence or absence of pericardial tamponade was documented in 77 patients. Patients with tamponade had a survival of 73% (24/33) compared to 11% (5/44) in those without its protective effect. The presence of tamponade improved survival (p less than 0.05) following stab injuries (77% vs. 29%), gunshot wounds (57% vs. none), right heart wounds (79% vs. 28%), left heart injuries (71% vs. 12%), and overall in patients arriving with vital signs (96% vs. 50%). Multivariant discriminant analysis by logistic regression demonstrated cardiac tamponade was a critical independent factor in patient survival, and suggested that it may be more influential than presenting vital signs in determining outcome.