When cardiac arrest occurs, patients have a better chance of surviving the sooner they can be defibrillated -- shocking the heart back to a normal rhythm.

The AED is used to defibrillate or reverse a potentially fatal, abnormal heart rhythm called ventricular fibrillation.

Trained providers may put in endotracheal breathing tubes; start intravenous lines; deliver sophisticated cardiac drugs; and defibrillate patients manually.