A 49-year-old woman was referred to our laboratory for a stress echocardiogram. She had been in her usual state of health until 3 months prior, when she had palpitations and mild dyspnea on exertion. Her history was significant for ductal breast carcinoma, for which she had undergone mastectomy several years ago. Her physical examination and electrocardiography results were unremarkable. On her resting echocardiogram a very large mass (6 6 cm) was noted in the right atrium (Figure 1). The mass was solid, sessile, and occupied the entire right atrium. The interatrial septum was indented by the mass. Based on this finding the stress test was cancelled and the patient was referred for operation. The patient underwent resection of the tumor, which was attached to the right atrial wall, parallel to the atrioventricular groove, and filled the entire right atrium. The mass was resected completely with the attached atrial wall tissue, and there was reconstruction of the coronary sinus to the right atrium with closure of the surgically created atrial septal defect. The operative and postoperative course was unremarkable, and the patient was discharged home in good condition. Pathologic examination of the resected mass demonstrated proliferation of enlarged vessels filled with blood, consistent with cavernous hemangioma (Figure 2).