Formation of thrombi on a permanent pacemaker lead is a rare complication of pacing. However, because of its serious outcome it should be suspected in a patient who reveals right-sided heart failure, dyspnea, or syncope. An early decision to perform an echocardiographic examination, followed by surgical or thrombolytic treatment can solve this clinical problem. In a 69-year-old woman with increasing signs of congestive heart failure, echocardiography revealed a mobile mass in the right atrium attached to the pacemaker lead. Because of threatened symptoms and large dimensions of the mass, urgent surgical removal of the endocardial lead was successfully performed.