A 60-year-old woman reported a 2-week history of dyspnea. She had a history of radiation therapy of the chest wall due to Hodgkin’s lymphoma 40 years prior, and a history of cardiac tamponade 1-year prior (Figure 1A and B). A hemorrhagic pericardial effusion (PE) was drained at that time. There were no atypical cells in pericardial fluid cytology. Serum tumor markers such as SCC (TA4) and CYFRA 21-1 were elevated, but computed tomography (CT), positron emission tomography (PET)-CT, and endoscopic evaluation findings were negative for malignancy (Figure 1C and D). Also, there was no evidence of infection or autoimmune disease in the pericardial fluid analysis and laboratory test. She was treated with steroids for 3 months and was doing well without any symptoms. Follow-up transthoracic echocardiography (TTE) showed resolved PE (Supplementary Video 1). However, she complained of new-onset dyspnea symptoms. TTE revealed minimal PE and more aggravated pericardial adhesion with septal bouncing and respiratory variation of mitral inflow (36%) (Figure 1E and F, Supplementary Videos 2 and 3). CT demonstrated diffused pericardial thickening with enhancement and newly developed necrotic masses at the left atrium and right atrioventricular grove (Figure 1G and H). PET-CT revealed multiple hyper-metabolic masses at the pericardium (Figure 1I and J). An open biopsy was performed and the patient was diagnosed with epithelioid angiosarcoma (Figure 1K and L). The patient was administered chemotherapy with doxorubicin. Cardiac malignancy is a rare disease, but it should be considered in patients with unexplained PE and constrictive pericarditis. For these patients, multimodality imaging is helpful for diagnosis.