In a 61 year old male with heart failure and pulmonary congestion the x-ray shows a right paracardial tumor. The patient suffered from a blunt chest trauma 6 years ago. Since that accident he complains about exercise related dyspnea and cardiac arrhythmia with atrial fibrillation. On echocardiography we found a echolucent cystic tumor with a solid center structure surrounded by a thin membrane. Doppler echocardiography revealed a heart cycle dependent flow at its margin. During dextrocardiography rapid opacification only of the peripheral structures of the tumor could be observed. These findings are consistent with a traumatic rupture of the right atrium, and the diagnosis of a posttraumatic aneurysma spurium of the right atrium was established. Surgery confirmed this diagnosis and the aneurysm was extirpated.