Congenital pericardial defect is a rare and little-known anomaly. Here we describe the unique clinical presentation of a 64-year-old man with partial defect of the left pericardium associated with ruptured acute type A aortic dissection manifesting massive left hemothorax. In this patient, the pericardial defect played the role of a pericardial draining window, which incidentally prevented the heart from cardiac tamponade. Emergent surgery was successfully performed with a prosthetic graft replacement.