A previously healthy 34-year-old man presented with progressive dyspnea and chest pain after viral infection. Initial transthoracic echocardiography (TTE) depicted massive pericardial effusion and he underwent pericardiocentesis of 900 mL serosanguinous fluid without identifiable malignant cells. Pericarditis-associated pericardial effusion was initially impressed. Nevertheless, follow-up TTE 3 months later demonstrated recurrent pericardial effusion without identifiable pericardial mass. Cardiac magnetic resonance (CMR) imaging revealed a huge mass, located at pericardial space with right atrial compression (Figure 1A), which was also revealed by transoesophageal echocardiography (Figure 1B). A firm tumor in size of 5.5×4.5 cm, which severely adhered to the pericardium and extended to right atrial wall, superior vena cava and aorta, was excised (Figure 1C). The pathologic examination confirmed the diagnosis of primary pericardial angiosarcoma, given the presence of malignant endothelial cells mainly in pericardial soft tissue (Figure 1D and E). Therapy with pembrolizumab and pazopanib was administered. Unfortunately, CMR revealed the recurrence of tumor 4 months after the surgery, and salvage radiotherapy was performed.