A simplified illustration of an Automated External Defibrillator (AED) with  electrode pads applied to a human figure.


Sudden cardiac arrest occurs when the heart suddenly and unexpectedly stops pumping blood. It can happen to anyone, at any time, and signs include sudden collapse and immediate loss of consciousness.

Unlike heart attacks, which are caused by a blockage in an artery to the heart, sudden cardiac arrest is caused when the heart’s electrical system malfunctions. This produces abnormal heart rhythms, called arrhythmias, that make the heart unable to pump blood.

If cardiac arrest does occur, rapid treatment with a medical device called an automated external defibrillator (AED) can be life-saving.

An AED is a type of computerized defibrillator that automatically analyzes the heart rhythm in people who are experiencing cardiac arrest. When appropriate, it delivers an electrical shock to the heart to restore its normal rhythm.  The conversion of a ventricular arrhythmia to its normal rhythm by an electrical shock is called defibrillation.

Defibrillation is time-sensitive. The probability of survival decreases by 7 percent to 10 percent for every minute that a victim stays in a life-threatening arrhythmia.

The U.S. Food and Drug Administration (FDA) regulates AEDs as medical devices and evaluates them for safety and effectiveness before they are marketed. 

Many AEDs Are in Plain Sight

You can find AEDs in many public places, including offices, schools, shopping malls, grocery stores, and airports.

Emergency first-responders are typically equipped with and trained to use AEDs. Some people with underlying cardiac conditions can be at a higher risk of sudden cardiac arrest. Your health care provider can tell you if a home AED is something you should consider. 

How AEDs Work

An AED system includes an AED device and accessories, such as a battery, pad electrodes, and if applicable, an adapter. The devices give verbal instructions to users.

This is how they work:

  • The user turns on the AED and follows the voice prompts. Some devices turn on automatically when the user opens the lid.
  • The user attaches two sticky pads with sensors (called electrodes) on the chest of the person in cardiac arrest.
  • The electrodes send information about the person’s heart rhythm to a processor in the AED, which then analyzes the rhythm to find out whether an electric shock is needed.
  • If a defibrillation shock is needed, the AED uses the voice prompts to instruct when to press a button to deliver the shock. In some devices, the voice prompts announce that a shock is going to be delivered and the AED delivers the shock without intervention by the user.

Training to Use AEDs

AEDs are not difficult to use, but training in the use of AEDs is highly recommended. This training, in connection with CPR training, is offered by many major health organizations. Some training is available online.

Classes can teach you how to recognize the signs of a sudden cardiac arrest, when to call emergency medical services, how to do CPR, and how to use an AED.

Some people may be afraid to use an AED because they’re worried something may go wrong. But most states’ Good Samaritan laws and the Federal Cardiac Arrest Survival Act provide some protection for bystanders who respond to emergencies.

But as always, in an emergency, call 911 immediately. If you’re somewhere that has an emergency response system that includes a clearly visible number, call that number for assistance. In either case, an operator can give instructions on how you can help someone who has sudden cardiac arrest.

How the FDA Regulates AEDs

As part of its regulatory oversight, the FDA closely monitors reports of device malfunctions, and reviews reports from consumers and manufacturers of AEDs.

Although the FDA regulates AEDs as medical devices, it does not regulate the resuscitation guidelines for the use of these devices. Visit this American Red Cross website to learn how and when to use an AED.

In February 2015, the FDA required manufacturers to have “premarket approval” before marketing AED devices and accessories necessary for the functionality of the AED, to better ensure quality design and manufacturing practices. Premarket approval is the most stringent type of device marketing review required by the FDA, and approval is based on a determination by the FDA, relying on valid scientific evidence, that there is a reasonable assurance that the device is safe and effective for its conditions of use.

The FDA maintains a list of AED devices that are FDA-approved. Certain AEDs that do not appear on the FDA-approved list are considered “legacy devices.” Although some of these legacy devices are still in use, they may no longer be legally marketed.

What this means for you:

If you own an AED, check the FDA’s list of approved AED devices to confirm the device is FDA-approved. Contact the AED manufacturer with any questions or concerns.

If a cardiac arrest emergency happens and an AED is available, know that AEDs can save lives, even legacy devices. The potential life-saving benefits of FDA-approved AEDs when used as intended outweigh the probable risks of using them, when accompanied by adequate directions and appropriate warnings. You should be confident in using these devices in life-threatening situations.

Report Device Problems to the FDA

Health care professionals and patients are encouraged to report adverse events or side effects related to the use of these products to the FDA’s MedWatch Safety Information and Adverse Event Reporting Program:

If you have questions about an AED device or AED accessory, contact the manufacturer. You can also call the FDA Consumer Complaint Coordinator who works with your state; phone numbers are listed online.