How to Use an AED Device: A Step-by-Step Guide for Bystanders and Responders

An automated external defibrillator (AED) is a portable device that checks a person's heart rhythm and, if needed, delivers an electric shock to restore an effective rhythm. This guide gives you the exact sequence for how to use an AED device on an adult, child, or infant in sudden cardiac arrest. Sudden cardiac arrest is not the same as a heart attack: the heart's electrical system malfunctions and the heart stops pumping blood effectively, so the person collapses and stops breathing normally. You do not need certification to use an AED, and the device speaks to you at every stage. Hands-on practice in a CPR/AED class builds speed and confidence, but the most important requirement is a willingness to act.

Step 1: Confirm Cardiac Arrest and Call 911

Start by checking responsiveness. Tap the person firmly on the shoulders and shout, "Are you okay?" At the same time, look at the chest for no more than about 10 seconds. If the person is not breathing, or is only gasping, treat it as cardiac arrest. Gasping (sometimes called agonal breathing) can look like snoring or gulping and is not normal breathing. It is common in the first minutes of cardiac arrest, and it fools many bystanders into waiting.

Next, get help moving. If you are alone, call 911 yourself. If other people are present, point at one person and give a direct instruction: "You in the blue jacket, call 911 and stay on the line. You by the door, find the AED and bring it back." Naming or pointing at people works far better than shouting to the crowd, where everyone assumes someone else has already acted.

Put the phone on speaker and set it next to you. The dispatcher can confirm the address, coach you through compressions, and talk you through the AED if you get stuck. Keep your hands free for the person on the ground.

Mistake to avoid: waiting to see whether the person recovers on their own. In cardiac arrest, every minute without compressions and defibrillation lowers the chance of survival. If you are unsure whether it is cardiac arrest, act anyway. Giving compressions to someone who turns out not to need them is far less harmful than withholding them from someone who does.

Step 2: Start Chest Compressions While the AED Is Retrieved

Do not wait for the AED to arrive before you begin. Compressions keep oxygenated blood moving to the brain and heart until a shock can be delivered. Lay the person on their back on a firm, flat surface, such as the floor, not a bed or sofa.

For an adult, follow this technique, which is consistent with American Heart Association and American Red Cross guidance as of 2026 (for a deeper walkthrough, see our guide on how to perform CPR on adults):

Kneel beside the person's chest.

Place the heel of one hand on the center of the chest, on the lower half of the breastbone. Put your other hand on top and interlace your fingers.

Lock your elbows and position your shoulders directly over your hands.

Push straight down at least 2 inches (about 5 cm), but not much more than 2.4 inches.

Compress at a rate of 100 to 120 per minute, allowing the chest to fully recoil between pushes.

A helpful pacing cue is the beat of "Stayin' Alive" by the Bee Gees. Push hard and fast, and do not lean on the chest between compressions.

If you are trained and willing, give two rescue breaths after every 30 compressions (the 30:2 ratio). If you are untrained or uncomfortable with breaths, hands-only CPR, meaning continuous compressions, is acceptable and far better than doing nothing.

Keep going until the AED is open, powered on, and telling you to stop. Interruptions in compressions reduce the blood flow you are working to build. Children and infants need modified technique: for a child, use one or two hands and compress about one-third the depth of the chest (roughly 2 inches); for an infant, use two fingers or two thumbs and compress about 1.5 inches (see our guide to infant CPR techniques for the full method). The same rate applies.

Step 3: Turn On the AED and Follow the Prompts

As soon as the AED arrives, place it next to the person's head or shoulder, on the side where you or a second rescuer will be working. If a second person is available, they set up the AED while you continue compressions. If you are alone, the dispatcher may tell you to pause briefly to set it up.

Open the carrying case, or lift the lid, and turn the device on. Some models power up automatically when the lid opens; others have a green power button you must press. Once it is on, the AED gives clear voice instructions, sometimes with screen text or lights. Listen and follow them rather than guessing. The device is designed for people with no training. If you want a slower, beginner-focused walkthrough, our guide on how to use an AED machine covers the basics step by step.

Public-access AEDs are often kept in wall cabinets. Opening the cabinet may set off an alarm. That is normal and is meant to draw attention, so do not let it rattle you or make you hesitate.

AED models differ slightly. Button placement, the shape of the shock button, pad connector location, and whether the unit is semi-automatic (you press a button) or fully automatic (it shocks on its own) all vary by manufacturer. The core sequence is the same on every device. If you work in a building with an AED, take a few minutes now to open the case and look at it, so the layout is familiar before you ever need it.

Step 4: Prepare the Chest and Place the Pads

The pads must touch bare, dry skin. Remove or cut away clothing, including bras with metal underwires, which can interfere with pad contact. Most AED kits include trauma shears and a small towel; use them. Wipe away heavy sweat or moisture. Shave chest hair only if it is thick enough to stop the pads from sticking, and only if a razor is immediately available. Otherwise, press the pads down firmly, or if the kit has a second set, use that to pull hair off and then apply fresh pads.

Standard adult placement

Peel the backing off each pad and follow the diagram printed on it. One pad goes on the upper right chest, just below the collarbone. The other goes on the left side of the chest, below the armpit, along the ribs. Press each pad down firmly. If the device prompts you to plug in the pad connector, push it into the marked socket.

Children and infants

For children under about 8 years old or weighing less than about 55 pounds, use child pads or a child setting if the AED has one. Do not let the pads overlap. If they are too close, place one on the center of the chest and the other on the center of the back. For infants, AHA guidance prefers a manual defibrillator, then an AED with a pediatric dose attenuator, then an AED with adult pads if nothing else is available. Use front and back placement for infants. Do not delay a shock because pediatric equipment is missing.

Special situations

Implanted device: if you see or feel a hard lump under the skin (a pacemaker or ICD), place the pad at least an inch away from it.

Medication patch: remove it and wipe the skin before applying the pad.

Wet surface: dry the chest. If the person is lying in water, move them to a dry area first.

Step 5: Let the AED Analyze and Clear the Area

Once the pads are on and connected, the AED will say something like "Analyzing heart rhythm, do not touch the patient." At that point, stop compressions and take your hands off the person. Movement, including compressions, can interfere with the reading and cause the device to misjudge the rhythm or delay its decision.

Say loudly, "Everyone clear," and look quickly to confirm that no one is touching the person, including anyone holding the head or giving breaths. Analysis usually takes only a few seconds.

This is the step that reassures many first-time users: the AED makes the decision, not you. It shocks only rhythms that can be corrected by a shock (ventricular fibrillation and certain fast ventricular tachycardias). If the person has no heartbeat at all, or does not need a shock, the AED will not allow one to be delivered. You cannot accidentally shock someone who does not need it.

Check the surroundings once more. If the person is on a wet surface, in standing water, or near puddles, move them to a dry spot before analysis and shock. Dry the chest if it is wet. Rain on a dry surface is less of a concern than standing water, but protect the person and the pads from direct soaking where you can.

Mistake to avoid: continuing compressions or "just adjusting" the person's position while the machine analyzes. Wait for the prompt, then act on what the AED says.

Step 6: Deliver the Shock or Resume CPR as Directed

The AED will announce one of two results.

If a shock is advised, the device will charge and tell you to stand clear. Do one last visual check that nobody is touching the person, say "Clear," and press the flashing shock button. Fully automatic models deliver the shock themselves after a countdown or warning, and you do nothing except stay clear.

Immediately after the shock, resume chest compressions, starting with the first push. Do not stop to check for a pulse or breathing. The heart often needs time and circulation after a shock before it resumes effective pumping, and checking wastes seconds that matter.

If no shock is advised, that does not mean the person is fine. It means the rhythm is not one a shock can fix. Begin CPR right away and keep following the prompts.

Many first-time users worry about hurting the person or being shocked themselves. Modern AEDs deliver a biphasic shock, meaning the current flows in one direction and then reverses, which treats the heart effectively at lower energy than older designs. The shock passes through the chest between the pads. If everyone is clear, it is safe for rescuers. A brief muscle jerk in the person is normal. Compressions that continue through analysis and shock are a larger risk than the shock itself, because they can disrupt the reading and expose the rescuer to the current.

Step 7: Continue the Cycle Until Help Takes Over

After the shock or the "no shock" message, the AED will prompt you to do CPR for about 2 minutes, then analyze again. Leave the pads in place and keep following the voice prompts. This cycle of 2 minutes of CPR, rhythm check, and shock if advised repeats until help arrives.

Compressions are physically demanding, and quality drops after a couple of minutes. If another person is available, switch compressors at each 2-minute rhythm check, keeping the swap under a few seconds. If you are alone, keep going as long as you safely can.

Stop only when one of these happens:

The person shows clear signs of life, such as breathing normally, moving, or opening their eyes.

Trained responders, such as EMS or firefighters, take over.

The scene becomes unsafe.

You are too exhausted to continue.

If the person starts breathing but is still unresponsive, keep the pads attached and monitor them closely. The AED may prompt you again if the heart rhythm changes.

When EMS arrives, give a short handoff: the time the person collapsed, how long CPR was performed, how many shocks the AED delivered, and that the AED is still attached. Leave the pads on and do not turn the device off. Paramedics may want to use the same pads or download the event data from the unit. If you manage an AED at work, remember that replacing AED pads on schedule and after every use keeps the device ready for the next emergency.

Turning What You Read Into Skills You Can Use Under Pressure

Reading the steps is a start, but practice is what makes them automatic. In a hands-on class, you handle a real trainer unit, feel proper compression depth, and rehearse pad placement until it takes seconds instead of minutes. Taylored Instruction teaches American Red Cross and American Heart Association CPR/AED courses and also sells AEDs for homes, workplaces, and facilities.

In the meantime, check the AED where you work or volunteer. Know where it is, confirm the status indicator shows it is ready, look at the battery and pad expiration dates, and make sure spare pads are on hand, including pediatric pads if children are present.

Don't wait until an emergency happens. Get the life-saving certification you need today. Register for a CPR, First Aid, or Lifeguarding class and gain the confidence and skills to respond when it matters most.