A battery powered cardioverter or defibrillator employing a DC-DC converter for charging high voltage output capacitors and for delivering biphasic cardioversion or defibrillation pulses through a bridge circuit including high and low side drive circuits under the control of a microprocessor controlled arrhythmia detection system. Upon the detection of an arrhythmia and the selection of cardioversion/defibrillation therapy, the charging of the high voltage output capacitors is commenced and the capacitor voltage enables a regulated voltage source for the high and low side drive circuits for the high power IGTs of each branch of the bridge circuit. High voltage switching transients are suppressed from re-triggering or otherwise affecting operation of the drive circuits. Fail-safe circuitry disables operation of the drive circuits in the event that the first and second control signals are inadvertently provided simultaneously or overlap.