It has been known since the 1930s that an electrical shock applied to the heart can stop ventricular fibrillation and restore the heart's normal rhythm.  In order to be useful as a life-saving technique, however, such a shock has to be applied within a few minutes after fibrillation begins.  Because early devices that applied this knowledge were large, expensive,  and required skilled operators, their applicability in practice was limited.

Research during the past two decades has led to the development of automatic external defibrillators (AEDs) that automatically analyze the heart's electrical signals to determine whether ventricular fibrillation is taking place, thus making them usable by people with far less training.  In addition, the newer devices are now small and inexpensive enough to be distributed widely in places where they might be needed: airplanes, workplaces, sports stadiums, and shopping malls.  The American Heart Association has been campaigning for wide placement of AEDs and the American Red Cross and other organizations have been offering training in their use.