Disclosed is an implantable catheter-type cardioverting electrode whose conductive discharge surface is comprised of coils of wound spring wire. An electrically conductive lead extends through the wound wire section of the electrode and has its distal end connected to the discharge coil at two locations. The proximal end of the conductive lead is adapted for connection to an implanted pulse generator. A pliable elastomeric material such as a medical-grade adhesive fills the conductive coils in the wound wire section of the spring wire electrode so that only the outer periphery of the wound section is exposed to the body. The catheter electrode is flexible, allowing easy implantation and avoiding trauma after implantation, and provides a large discharge surface for effecting defibrillation. The electrode is designed to reside in or about the heart, as in the superior vena cava or in the coronary sinus, and acts against another implanted electrode such as a conformal electrode residing at the apex of the heart.