Introduced about five years ago, external biphasic defibrillators have attracted a lot of attention. The biphasic waveforms they use have been shown in some studies to be more successful than standard monophasic waveforms in terminating ventricular fibrillation and ventricular tachycardia. But with this apparent step forward comes confusion: A variety of biphasic waveforms are available, and each defibrillator supplier is making claims for the superiority of its particular waveform. Are biphasic waveforms really better than monophasic? Is any one biphasic waveform preferable to another? What does the clinical literature say about this technology? This article answers those and other pressing questions about biphasic defibrillators.