We reported a 34-year-old man who was diagnosed as primary cardiac angiosarcoma. The diagnosis was delayed until one month after he first entered the hospital. Because cardiac angiosarcoma is easy to be misdiagnosed as pneumonia or other diseases due to its rarity. Although surgical therapy is always considered as a method that can prolong survival time, highly malignant tumors with local infiltration and systemic metastasis lead to poor prognosis. We stressed that primary cardiac malignancy should be noticed when a young patient presented as unexplained pericardial effusion or refractory pneumonia. Early diagnosis can provide more possibilities for treatments.