A case of rhabdomyosarcoma of the right atrium is presented. Fits of dyspnoea and cyanosis, provoked by postural changes, and pulmonary embolism were the most typical symptoms. Abnormal features were: the long history and the unspecific findings at auscultation and x‐ray examination. Histologically the part of the tumour contiguous with the atrial wall was composed of fairly well differentiated rhabdomyoblasts, while the part protruding into the atrium was anaplastic and necrotic. There were multiple pulmonary emboli, which originated from the anaplastic par