The permanently implanted automatic defibrillator offers an alternative treatment for heart patients with high risk of ventricular fibrillation, who cannot be safely treated by surgery or drugs. Because of size and energy requirements, permanently implanted automatic defibrillators are not presently practical for many of these patinets, and sudden death from ventricular fibrillation remains a majof health problem. This study, which determines the optimal electrode configuration of the transvenous catheter when used in conjunction with a subcutaneous plate or disk electrode for transvenous ventricular defibrillation, attempts one of many changes needed to improve the defibrillator's efficiency so that it will be a viable alternative treatment for delicate heart patients.