An automatic external defibrillator (AED) is:

• a lightweight, portable, battery-operated, computerized device resembling a colorful, over-inflated computer with a pair of self-stick pads called electrodes which are used to restore a regular heartbeat after sudden cardiac arrest (SCA) (a process called defibrillation) caused by undiagnosed heart problems or commotio cordis;
• Are suitable for use by trained lay persons. Such use is permitted by "Good Samaritan Laws" in every state, which generally protects the rescuer, the owner of the device and the medical director who oversees the program from civil tort liability. AEDs are specifically designed for use by non-medical personnel to revive people in cardiac arrest; and
• Are relatively inexpensive (less than $1,500).

Like defibrillators on TV, only automated

Most people are familiar with defibrillators from having seen them used on medical dramas and reality shows on television. A physician calls out a setting, makes sure no one is touching the unconscious victim ("Clear!"), and holds a set of paddles on the victim's chest while someone else delivers a shock.

AEDs do the same thing, except the machine itself determines how strong a shock is given (and if it is needed at all), the sticky pads take the place of the paddles, and the operator presses the Shock button after making sure no one is touching the victim. Unlike manual defibrillators used by paramedics and physicians, the important decisions are made by the AED.

How an AED works

Once an AED is turned on and the pads are placed on the victim's bare chest (one about halfway between the right nipple and the right collarbone and the other on the left side about two inches below the left armpit), it immediately begins analyzing the victim's heart rhythm and providing directions to the operator, via both spoken and text directions displayed on a faceplate on the AED itself). If the AED senses that the victim is in cardiac arrest, it advises the operator in a matter of seconds to push a button to deliver a shock.

Next to foolproof

As long as an AED is turned on, it is designed to be next to foolproof:

• It will not prompt the operator to go to the next step until the previous step has been completed;
• It provides a direction sequence that is so logical, well-defined, and well-documented, that rescuers remain calm, even those with little or no experience in responding to cardiac emergencies. One study showed that 6th grade students with a brief orientation to the device could safely administer a shock in a time no longer than highly skilled paramedics. It takes only about 4 hours of training to be certified to use an AED; 
• It will not allow a shock to be administered unless the person is actually in cardiac arrest.