Automated External Defibrillators have gained considerable notoriety lately, as airlines, businesses, and public facilities have purchased the devices in case of emergency. In several well-publicized cases, the devices have saved lives.

Here's how they work:

When a person experiences sudden cardiac arrest, his or her heart stops pumping blood. Medically speaking, the heart may still beat, but it's unsynchronized instead of the usual, uniform "lub-dub."

This condition is called ventricular fibrillation, or "v-fib." Doctors say the heart looks like a squirmy bag of worms when it's in v-fib. Its electrical impulses are misfiring, and different sections of the heart twitch at different times.

A defibrillator places a shock of electricity across the heart to jolt it back into a normal "rhythm."

While, unfortunately, AEDs don't always work, companies are investing them because they know the sooner a patient receives CPR and defibrillation, the better that person's chances of making a full recovery. Since a heart in v-fib isn't really pumping blood, a patient will have no pulse and will quit breathing. Without immediate first aid, the patient's body will be deprived of oxygen too long, and resuscitation will be impossible.

Only CPR will keep the patient alive until defibrillation occurs. CPR by family, friends, and passers-by and a call to 9-1-1 are the first two links of what we in the emergency medical system refer to that as the "chain of life."