A 79-year-old man who was in normal sinus rhythm with a palpable pulse was inappropriately shocked twice by a fully automated external defibrillator. The second shock resulted in ventricular tachycardia. The device then countershocked a third time, restoring normal sinus rhythm. The problem occurred primarily because the rescuers did not follow the device's instructions warning against applying the device in analysis mode to a patient with a palpable pulse, and they attempted to analyze the rhythm in a moving vehicle. Motion artifact and T waves that were relatively tall compared with the QRS amplitude were misinterpreted as ventricular fibrillation by the device. This example of inappropriate countershocks delivered by rescuers using a fully automated device illustrates the importance of proper training and continuing education.