Defibrillator : Device that can deliver a therapeutic electric shock to the heart. Defibrillators are often used to restart the heart if it is in a dangerous arrhythmia such as ventricular fibrillation.

Automated External Defibrillator (AED) : A device that automatically analyzes the heart rhythm and, if it detects a problem that may respond to an electrical shock, that permits a shock to be delivered to restore a normal heart rhythm.