A 37-year-old woman who sustained blunt chest trauma as a result of a car accident was found unconscious at the accident site with signs of circulatory compromise. Computed tomographic trauma screening excluded thoracic, intracranial, and intra-abdominal bleeding, or other pathologic findings, except a small circumferential hemopericardium. Echocardiography revealed a hemopericardium that was partially clotted and the beginning of compression of the right ventricle. Because of progressive hemodynamic compromise, the decision was made for operative exploration. After a median sternotomy, the resultant excessive bleeding necessitated extracorporeal circulation. Careful inspection revealed isolated rupture of the upper right pulmonary vein, which was successfully repaired.