A defibrillator is a device that delivers electric shock to the heart when it has an abnormal rhythm (arrhythmia). External defibrillators include pads placed on the chest to deliver electric shock. Internal defibrillators (implantable cardioverter defibrillators, or ICDs) look similar to a pacemaker; they continuously monitor the heart rhythm to detect overly rapid arrhythmias such as ventricular tachycardia or ventricular fibrillation. The ICD corrects the heart rhythm by delivering precisely calibrated and timed electrical shocks to restore a normal heartbeat when one of these dangerous arrhythmias has occurred.

Return to Encyclopedia Home Image