Cardiac arrest is the sudden loss of heart function. The victims aren't breathing and have no pulse rate, and doctors consider them clinically dead, though there is a window of less than 10 minutes during which there is a chance of survival.
Defibrillators for years have been used to reverse one of the most common types of cardiac arrest, ventricular fibrillation, by delivering an electric shock that kick-starts the heart back into syncopated rhythm. The rescuer fires a back-arching blast of voltage through a pair of electrodes pressed against the victim's chest.
Yet an estimated 250,000 Americans die every year mainly because rescuers can't reach them in time. The American Heart Association declared war on the disease in 1994 by urging medical manufacturers to build a simple device that could be posted in public places.