Between September of 1991 and February of 1996, 108 patients with penetrating wounds near the heart, and with no obvious signs of cardiac injury, underwent the creation of a diagnostic thoracoscopic pericardial window to rule out cardiac injury. In 33 patients (30.6%), the procedure identified hemopericardium. Sensitivity for the procedure was 100%, specificity 96%, and accuracy 97%. There were no deaths and no complications due to the procedure. The thoracoscopic pericardial window has proved to be a precise, rapid, and safe method for the diagnosis of heart wounds in patients with no clear signs or symptoms, and it also allows the evaluation of other thoracic injuries and the evacuation of hemothorax when present. We recommend this procedure as the standard diagnostic approach for cardiac injuries in patients in stable condition.