An AED (automated external defibrillator) is a device that delivers an electric shock to the heart of a person in cardiac arrest. The device is very simple to operate since it gives verbal instructions on how to use it. All you have to remember is to turn it on. The AED is a "smart" device and will only deliver a shock when it is needed.
When a person collapses in cardiac arrest the heart is often in a rhythm called ventricular fibrillation. This rhythm is fatal unless an AED is applied which can stop the fatal rhythm and change it to a normal rhythm. An electric shock delivered quickly by an AED can be life saving.
An AED should be used whenever you see a person collapse or become unconsciousness and who does not respond to your shouting or shaking. It should also be used if you come upon a collapsed person even if you didn't see that person collapse.
Speed is crucial. The AED must be attached as quickly as possible. Call 911, tell the operator you have an AED and then bring it to the collapsed person. Turn it on and follow verbal directions. Every minute of delay decreases the person's chances of survival by 7% to10%.