Traumatic cardiac rupture is mostly accompanied by tamponade and/or hemopericardium. We experienced a rare case of traumatic right atrial rupture with left hemothorax, but without hemopericardium. A 36-year-old male had a traffic accident, and was transported to our hospital. He was in a state of shock caused by massive hemothorax. He underwent emergency operation through median sternotomy. No blood was seen in the pericardium nor injury of any major vessels or lungs. When the heart was exposed, massive bleeding occurred. A tear of 30 mm in length was found in the right atrium at the junction of the superior vena cava. The tear was repaired under cardiopulumonary bypass. Even after surgery, however, he remained unconscious.