A 68-year-old woman, known to have a secundum atrial septal defect which had been asymptomatic, reported dyspnea and occasional chest pain for two years. Admission examination revealed orthopnea, cyanosis, polycythemia and inflow congestion of the upper part of the body. After some blood-letting, nifedipine and nitrates brought immediate relief of symptoms. Physical examination, chest x-ray and ECG were not different from previously known findings. All laboratory tests were normal. The findings on cross-sectional echocardiography raised the suspicion of a right ventricular tumor, which was then demonstrated by computed tomography. There were no metastases. Under extracorporeal circulation a right-ventricular benign myxoma, attached to the apical septum and the size of a tennis-ball, was removed. The postoperative course was without complications and the patient was discharged symptom-free.