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Biphasic truncated exponential (BTE) waveforms are used in all implantable cardioverter defibrillators, and are now being implemented in transthoracic defibrillators. Not all BTE waveforms are the same, and the direct comparison of BTE defibrillators is rare. In addition, humans exhibit a wide range of transthoracic impedance, and defibrillators compensate for this range of impedance in different ways. Here we compared the efficacy of the Life Quest BTE defibrillator made by Medical Research Labs., Inc. (MRL) to the LifePak 12 BTE defibrillator made by PhysioControl (PC) in an animal model that simulates higher impedance patients (which are reported to be associated with poorer outcomes with conventional defibrillators). We found the MRL BTE waveform was as effective as the PC BTE waveform on the basis of delivered energy, but required 22 percent less peak current in this model of simulated higher impedance patients.