An automated external defibrillator (AED) is a portable automatic device used to restore normal heart rhythm to patients in cardiac arrest.

An AED is applied outside the body. It automatically analyzes the patient’s heart rhythm and advises the rescuer whether or not a shock is needed to restore a normal heart beat. If the patient’s heart resumes beating normally, the heart has been defibrillated.

Heart attacks and other conditions can cause ventricular fibrillation. In ventricular fibrillation, the electrical signals in the lower part of the heart are uncoordinated and ineffective. Very little blood is pumped from the heart to the body or the lungs. If ventricular fibrillation is not treated, it will result in Cardiac Arrest.

You can find AEDs in public places, such as airports and office buildings (public access AEDs). Doctors sometimes recommend home defibrillators for patients with heart disease.

An AED consists of a small computer (microprocessor), electrodes, and electrical circuitry. The electrodes collect information about the heart’s rhythm. The microprocessor interprets the rhythm.

If the heart is in ventricular fibrillation, the microprocessor recommends a defibrillating shock. The shock is delivered by adhesive electrode pads, through the victim’s chest wall, and into the heart.

There are special low-power electrode pads for use on children.

Most trained users can operate AEDs safely. There is some risk of electric shock to the operator and others if the operator has not been trained to avoid touching the patient. Other risks include skin burns from the electrodes, abnormal heart rhythms, and blood clots.

The device should not be used in a patient who has a pulse. It should also be avoided under conditions where the patient cannot be isolated from other people (for example, in the standing water of a rowboat that is filled with passengers who are either touching the patient or the water).

Find information about specific automated external defibrillators from FDA's Recently Approved Devices listings.

• AEDs and Public Access Defibrillation Programs
  US Food and Drug Administration
  http://www.fda.gov/cdrh/consumer/AED_PAD.html