Prognosis of angiosarcoma, the most common primary malignant cardiac tumor, is very poor. An early detection and treatment may extend survival beyond one year. Newer imaging modalities, including magnetic resonance imaging (MRI), play an important role in the evaluation of cardiac masses. The case of a man admitted to the emergency room for a cardiac tamponade is reported. Thoracic computed tomography and MRI diagnosed a pericardial tumor, for which surgical biopsy revealed an angiosarcoma. Chemotherapy was started, and the patient survived for 28 months. Etiologies of hemorrhagic tamponades are discussed, as well as treatment of cardiac angiosarcoma.