We investigated in sheep, non-thoracotomy extraction of leads which had been chronically implanted in the right atrium (RA), coronary sinus/great cardiac vein (CS/GCV) and right ventricle (RV) for atrial implantable defibrillation. Clinical success of extraction as well as gross and histologic findings in the heart are reported. Six of nine sheep had successful extractions. The major complication was laceration of the wall of the great coronary vein with hemorrhage into the pericardial space and cardiac tamponade. Tissue damage included several reversible changes: intra-tissue hemorrhage, thrombosis in the veins, and some necrosis of fat, vascular wall and myocardium. Myocyte necrosis was estimated as 0.03 to 0.3 grams of tissue. Osseous and cartilaginous metaplasia was more common around the RA lead than the CS/GCV lead. In cases where the lead must be removed, removal from the venous insertion site using lead extraction equipment should only be attempted with surgical back-up for emergency thoracotomy to control hemorrhage in the event of vessel laceration. Safer explantation of these leads from the vein entry site will require the development of new extraction procedures.