Abstract: An implantable cardiac ventricular defibrillation system based upon entirely endovascular placement of a minimal number of electrodes is disclosed. The electrodes are designed to deliver a number of subpulses that are rapidly switched within an overall defibrillation shock envelope. The rapid switching between set pairs of electrodes achieves an overall electric field strength and distribution that is optimized for lowest threshold defibrillation energies and voltages. The defibrillation system also incorporates a system and method for optimally tuning and correlating the parameters of the subpulse delivery to the individualized needs of a human subject. The implantable defibrillation system reduces the energy and voltage levels needed for successful ventricular defibrillation in a clinically feasible manner.