How to Use an AED: A Step-by-Step Guide for Bystanders
An automated external defibrillator, or AED, is built so that an untrained bystander can save a life with it. That is the whole point of the device. It talks you through every step, decides for itself whether a shock is needed, and will not let you do harm. If you can follow spoken instructions, you can use an AED.
This guide walks through exactly what to do, in order, so the device feels familiar before you ever need it. Sudden cardiac arrest gives no warning, and survival drops with every passing minute — so the most valuable thing you can do is know the sequence in advance.
What an AED actually does
During sudden cardiac arrest, the heart’s electrical rhythm becomes chaotic and it stops pumping blood effectively. An AED reads that rhythm through adhesive pads placed on the chest, and if it detects a shockable rhythm, it delivers a measured electrical shock to reset the heart. Crucially, the AED will only allow a shock when one is genuinely needed — you cannot accidentally shock someone who does not require it.
If someone collapses, is unresponsive, and is not breathing normally, call 911 (or have someone else call) and send for the nearest AED immediately. Begin CPR if you are able. The AED works alongside CPR, not instead of it.
The five steps to using an AED
1. Turn it on
Open the lid or press the power button. From this moment the device speaks to you. Every modern AED — whether it’s a Philips HeartStart, a ZOLL AED Plus, or a Cardiac Science Powerheart — guides you with clear voice prompts and, on many models, visual cues. Listen and follow along. You do not need to memorize anything.
2. Expose and prepare the chest
Remove or cut away clothing to bare the chest. The skin needs to be dry and bare for the pads to make contact, so wipe away sweat or water and, if the chest is very hairy where a pad sits, shave it quickly with the razor included in most AED kits.
3. Apply the pads
Peel the electrode pads and place them firmly on bare skin exactly as shown in the diagrams printed on each pad — one on the upper right chest below the collarbone, the other on the lower left side below the armpit. For a child under eight or under roughly 55 pounds, use pediatric pads if available. Pad placement is the one step people worry about, and the device removes the guesswork: just match the pictures.
4. Let the AED analyze
The AED will say “analyzing heart rhythm — do not touch the patient.” Make sure no one is touching the person, including you. The device is now deciding whether a shock is needed. This takes only seconds.
5. Deliver the shock, if advised
If the AED advises a shock, it will tell everyone to stand clear. Confirm no one is touching the patient, then press the flashing shock button (on a fully automatic model, it delivers the shock on its own). Immediately resume CPR — chest compressions — and continue following the prompts until EMS arrives and takes over.
You cannot do it wrong. The AED will not shock a heart that doesn’t need it, and doing something dramatically beats doing nothing. Survival from witnessed cardiac arrest more than triples when a bystander acts with CPR and an AED.
Why every facility should have one within reach
An AED only saves a life if it’s close enough to use in the first few minutes. That’s why schools, offices, gyms, and houses of worship are placing devices in visible, central locations — and why pad and battery readiness matters as much as the device itself. A device with expired pads cannot help anyone.
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Frequently asked questions
Can I use an AED without training?
Yes. AEDs are designed for untrained bystanders. The device provides spoken step-by-step instructions and will only permit a shock when the heart’s rhythm requires one. Formal CPR/AED training builds confidence and is recommended, but it is not required to act in an emergency.
Can an AED hurt someone who isn’t in cardiac arrest?
No. An AED analyzes the heart rhythm and will not deliver a shock unless it detects a shockable rhythm. If no shock is needed, the device will not allow one.
Where should AED pads be placed?
One pad goes on the upper right chest just below the collarbone, and the other on the lower left side below the armpit. Diagrams printed on each pad show the exact placement. Use pediatric pads for children under roughly eight years old or 55 pounds when available.
Do I still need to do CPR if I have an AED?
Yes. CPR and an AED work together. Perform chest compressions until the AED is ready, follow its prompts, and resume CPR immediately after any shock until emergency responders arrive.
