We report the case of a 55-year-old woman seen with signs of angina pectoris and dyspnea. Transesophageal echocardiography showed a floating thrombus distal to the right coronary ostium. At operation, we found a highly mobile thrombus attached to an atherosclerotic plaque distal to the right coronary ostium. The atherosclerotic lesion and the pedunculated thrombotic mass were removed without resection of the adjacent aortic wall. In our judgment, a floating mass in the ascending aorta represents an emergency and should be removed before major thromboembolic complications occur.