About 250,000 people die each year from sudden cardiac arrest. That 's 700 each day. Usually, cardiac arrest results from a type of heart rhythm irregularity called ventricular fibrillation. Ventricular fibrillation is a condition in which the heart's electrical impulses suddenly become chaotic, often without warning. That causes the heart's pumping action to abruptly stop, the victim loses consciousness, has no pulse and stops breathing normally.
Death follows within minutes.
Defibrillation, if done immediately after the heart stops, can restore the heart's normal rhythm and keep the victim alive. For every minute that passes without defibrillation, a victim's chances of survival decrease by 7 to 10 percent. After 10 minutes, very few resuscitation attempts are successful. In the past, only emergency medical personnel could defibrillate. Today, a new generation of defibrillators, called automated external defibrillators, makes it possible for trained lay rescuers to deliver defibrillation.