Currently, several different biphasic waveforms are in use for cardioversion.The comparative efficacy and safety of these waveforms has not been compared in clinical studies. Commercially available defibrillators use different electrical waveforms that may affect the efficacy of external defibrillation. Although the superiority of biphasic over monophasic waveforms is well established, the relative efficacy and safety of the available biphasic waveforms is not clear.