Health Library

Health Library

Automated External Defibrillator

When someone’s heart stops working, it is known as sudden cardiac arrest. Sudden cardiac arrest happens to many thousands of people each year. It causes blood to stop flowing to the brain and other organs. This can cause a person to die within minutes. But in some cases, an automated external defibrillator (AED) may save a person’s life.

What is an automated external defibrillator?

Picture shows an automated external defibrillator

An AED is a small, portable, battery-powered machine with a computer in it. The machine detects heart activity. It can give an electric shock to someone if needed. It uses small sticky electrodes that are put on a person’s body. The electrodes are attached to wires. The wires send information from the body to the AED machine. The machine checks the heart’s electrical system. If certain kinds of arrhythmias are found, the machine can give the person an electric shock. This can reset the heart’s electrical activity and cause it to beat normally again.

How does an AED work?

The heart has its own electrical system. It controls how the heart contracts and pumps blood – or “beats.” Heartbeats are known as the heart rhythm. But sometimes a person can get abnormal heartbeats. These are known as arrhythmias. Some kinds of dangerous arrhythmias can cause sudden cardiac arrest. One is ventricular fibrillation. This causes the heart’s lower chambers to flutter instead of pump. They can’t move blood when this happens. Another dangerous arrhythmia is called ventricular tachycardia. This causes the heart’s lower chambers to pump too fast. It can also cause the heart to not pump blood.

An AED can detect these arrhythmias. It can then give an electric shock to the heart. This can help it restart at a normal rhythm. 

Using an AED

Anyone can use an AED. Many people -- such as first responders, flight attendants, and people who work in large public facilities – are trained to use an AED. But AEDs are also made to be used by people with no training. This is because it can save a person’s life in minutes. There may not be time to find someone who has training. All AEDs come with instructions. Many AEDs tell the user what to do with voice commands.

AEDs are found in many public places where a person may have sudden cardiac arrest:

  • Airports and airplanes

  • Ambulances

  • Casinos

  • Convention centers

  • Cruise ships

  • Fire engines

  • Grocery stores

  • Hotels

  • Offices

  • Police vehicles

  • Public pools

  • Schools

  • Shopping malls

  • Sports arenas

  • Trains and buses

You can also buy and learn to use an AED at home. You can find an AED training class in your area by contacting the American Heart Association at 800-242-8721 or

Automated External Defibrillator - WellSpan Health

Author: Wheeler, Brooke
Online Medical Reviewer: Foster, Sara, RN, MPH
Last Review Date: 2013-08-13T00:00:00
Published Date: 2014-04-29T00:00:00
Last Review Date: 2013-08-21T00:00:00
© 2015 WellSpan Health. All Rights Reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.

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