A 31-year-old woman was admitted to our hospital with a sudden onset of chest pain and dyspnea. Echocardiography, chest CT, and chest MRI revealed a huge mass in the right atrium. She underwent pericardial drainage to alleviate cardiac tamponade. Emergency surgery was performed because of superior vena cava syndrome and the risk of tricuspid valve obstruction by the mass. The tumor was resected en bloc, including the right atrial wall and a large segment of the proximal superior vena cava. The right atrium was then reconstructed with a Xenomedica patch and the superior vena cava was reconstructed using an expanded polytetrafluoroethylene (ePTFE) vascular graft. The pathological diagnosis was haemangiosarcoma. Cardiac angiosarcoma is a rare tumor, and its prognosis is very poor. The patient could survive for about 5 months after surgical resection.