Several consultant cardiologists were invited to assess the accuracy of the Lifepak 200 automated external defibrillator (AED) (Fig. 1), from ECG records collected from pre-hospital cardiac arrest victims. They were asked to classify the ECG rhythms, and also give an opinion on whether or not a shock should have been given, and the potential harm of inappropriate treatment. As there was no absolute agreement between cardiologists in rhythm classification, sensitivity of the AED for ventricular fibrillation varied from 78% to 100%, and the specificity was between 92% and 100% according to each cardiologist. They agreed that all ventricular fibrillation should be shocked and failure to do so would reduce a patient's chances of survival; and that all other rhythms, and asystole, should not be shocked. Most experts believed shocking asystole would not be harmful, but opinions regarding the potential harm of administering shocks to patients with pulseless rhythm were mixed.