In a 62-year-old man with permanent atrial fibrillation and recurrent stroke, a large right atrial thrombus attached to a permanent pacemaker lead was incidentally identified by transesophageal echocardiography. Surgical treatment, recommended because of the large dimensions of the mass, was refused by the patient, and thrombus was successfully dissolved by anticoagulant treatment. Pathogenesis of pacemaker lead thrombosis, clinical implications, diagnostic and therapeutic options are discussed.