A 49-year-old man was admitted for primary cardiac angiosarcoma with a cardiac tamponade. Transthoracic echocardiography and contrast-enhanced computed tomography scan demonstrated a large mass in the right atrium and thickening of the right ventricular wall. 18F-labeled deoxyglucose (FDG) positron emission tomography (PET) scan showed increased FDG uptake in the mediastinum and over the heart. The patient responded to combination therapy with docetaxel and radiotherapy and tolerated the treatment well, except for radiation esophagitis, which required a soft diet and resolved 1 month after treatment. This combination therapy resulted in a minimal response with slight regression in the tumor size, but FDG-PET initially showed an increase in FDG uptake by the tumor that was no longer seen after combination therapy. There is no evidence of progression or metastasis even at 12 months after diagnosis.