[Cardiac Angiosarcoma with Cardiac Tamponade due to Ruptured Right Atrium:Report of a Case].

Primary angiosarcoma of the heart is extremely rare with poor prognosis. A 39-year-old man presented to his physician for evaluation of fever and pericardial pain and was referred to our department for further management. The patient's condition stabilized after pericardiocentesis;however, the cause of cardiac tamponade remained undetermined on admission. Transesophageal echocardiography and electrocardiography-synchronized contrast-enhanced computed tomography (CT) revealed a suspected source of bleeding in the right atrium, necessitating open chest surgery. Preoperative imaging showed no evidence of a tumor;however, intraoperatively, we observed a suspected right atrial tumor, which was resected, followed by repair using a bovine pericardial patch. Histopathological examination confirmed diagnosis of angiosarcoma. Angiosarcoma is often diagnostically challenging in the early stages, and multiple examinations are important for early diagnosis and treatment.