How do you use an automated external defibrillator (AED)?

Defibrillators are devices that give a controlled electric shock and can be used to resuscitate someone whose heart has stopped suddenly.

Many companies, public spaces and buildings are equipped with automated external defibrillators (heart defibrillators) for first aid nowadays. These devices are easy to use, even if you haven’t ever come across one before. Defibrillators can often be recognized as such based on the abbreviation “AED” and/or a green sign with a heart symbol on it.

How do automated external defibrillators work?

An AED looks like a first aid box or a small toolbox. The box has two cables attached to it, each with a postcard-sized sticker on the end of it (the electrodes). The electrode pads connect the device to the unconscious person.

Defibrillators are easy to use in an emergency: The box gives spoken instructions, telling you what to do and in which order. Depending on the model, there may also be a small screen or diagrams to help you understand what to do.

When used properly, AEDs recognize two typical conditions of the heart that can make people lose consciousness and stop breathing, and can react accordingly:

  • Ventricular fibrillation: Here the heart muscle still contracts, but far too fast and in a chaotic way. As a result, the heart “twitches” rather than pumping, so it is no longer able to pump blood around the body. By exposing the heart to a controlled electric shock, defibrillators can restore a normal heartbeat, making the heart pump effectively again.
  • Lack of heart activity (asystole): Here the heart muscles stop contracting completely, and the heart stops pumping. Applying an electric shock won’t help in this case. Cardiac compressions are needed instead. The defibrillator then helps by giving spoken instructions.
Illustration: Defibrillator: a) Example of storage location, b) Taking out the AED case, c) An open AED case with adhesive electrode pads

When are defibrillators used?

You should use a defibrillator if you are resuscitating an unconscious person with the help of others. You can then share the different tasks: One person can start doing chest compressions, while the other person (or people) call for an ambulance and get the defibrillator.

If you are alone, call for an ambulance first and then immediately start doing chest compressions.

How are defibrillators used?

As soon as you get hold of a defibrillator, you have to turn it on and connect it. It’s important to continue doing chest compressions until the device tells you to stop. Work together: One person can continue with the chest compressions, while another person sticks the two electrodes on the naked chest of the unconscious person. One of the electrodes should be placed under the right collarbone, and the other should be placed on the left side of the chest – under the armpit. Then follow the spoken instructions given by the device.

Illustration: Using a defibrillator: a) Placing electrodes on chest and doing chest compressions, b) Pressing the shock button, making sure not to touch the unconscious person

If the defibrillator recognizes that someone’s heart is fibrillating, it will ask you to press the shock button to produce an electric shock. The shock button often has a “lightning” symbol on it. Follow the spoken instructions given by the device. It's important to make sure that neither you nor anyone else is touching the unconscious person when the shock button is pressed. Continue to follow the instructions given by the defibrillator afterwards – for instance, the device may tell you to do chest compressions again.

Deutsche Gesetzliche Unfallversicherung (DGU). DGUV-Information 204-010: Automatisierte Defibrillation im Rahmen der betrieblichen Ersten Hilfe. 2014.

Olasveengen TM, Semeraro F, Ristagno G et al. Basismaßnahmen zur Wiederbelebung Erwachsener (Basic Life Support). Leitlinien des European Resuscitation Council 2021. Notf Rett Med 2021 [Epub ahead of print]: 1-20.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Created on February 17, 2022

Next planned update: 2025


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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