How to Use an AED in a Cardiac Emergency

A person collapses at work, in a clinic waiting room, at the gym, or at home. They are unresponsive and are not breathing normally. In that moment, knowing how to use an AED can turn bystanders into an organized response team while emergency medical services are on the way.

An automated external defibrillator, or AED, is designed to guide a responder through the process with clear voice and visual prompts. You do not need to interpret the heart rhythm or decide whether a shock is appropriate. The AED analyzes the rhythm and advises a shock only when it detects a shockable rhythm. Your job is to act quickly, follow the prompts, continue high-quality CPR, and keep everyone clear when instructed.

Recognize when an AED is needed

Use an AED when a person is unresponsive and is not breathing normally, or is only gasping. Sudden collapse, no response to voice or touch, and abnormal breathing are warning signs of cardiac arrest. Gasping may look like breathing, but it is not normal breathing and should be treated as an emergency.

First, make sure the scene is safe for you, the person, and others nearby. Tap the person, shout to check for a response, and look for normal breathing for no more than 10 seconds. Healthcare professionals should also check for a pulse if trained to do so, but this assessment should not delay CPR or AED use.

Call 911 immediately, or direct a specific person to call. If others are present, assign clear tasks: one person calls 911, one gets the AED, and one begins CPR. Specific directions work better than calling generally for help. Say, “You in the blue shirt, call 911 and bring the AED.”

If you are alone and the AED is nearby, activate emergency response on speakerphone, retrieve the AED if possible, and begin care. The priority is early 911 activation, CPR, and defibrillation.

How to use an AED step by step

Start CPR as soon as cardiac arrest is recognized. Place the heel of one hand in the center of the chest, place your other hand on top, and push hard and fast at a rate of 100 to 120 compressions per minute. Let the chest fully recoil between compressions. If you are trained and willing to provide breaths, use cycles of 30 compressions and 2 breaths for an adult. If you are not trained in rescue breaths, provide hands-only CPR until more help arrives.

When the AED arrives, use it without unnecessary interruption to chest compressions.

1. Turn on the AED. Open the case or press the power button. Most units begin speaking as soon as they are opened or powered on. Listen to the device and follow its prompts exactly.

2. Expose and prepare the chest. Remove clothing from the person’s chest. If the chest is wet, dry it quickly so the pads will stick. If there is excessive chest hair where a pad must be placed, use the razor in the AED kit if available and remove only enough hair for pad contact. Do not delay defibrillation for minor issues.

3. Apply the pads as shown. Peel the backing from each adhesive pad and place them on the bare chest according to the diagrams. For most adults, place one pad on the upper right chest below the collarbone and the other on the lower left side of the chest, below the armpit. Press firmly so each pad adheres well.

4. Clear the person for analysis and shock delivery. When the AED says it is analyzing, stop compressions and make sure no one is touching the person. Say loudly, “Clear.” If the AED advises a shock, visually confirm that everyone is clear, then press the flashing shock button if the unit instructs you to do so. Some AEDs deliver the shock automatically after a warning.

Immediately resume CPR after the shock, starting with chest compressions. Do not stop to check for a pulse or wait to see whether the person wakes up unless they show obvious signs of life. The AED will tell you when to pause again for another rhythm analysis, usually after about two minutes of CPR.

Pad placement and special situations

AED pads must make direct contact with bare skin. Do not place pads over clothing, medication patches, or obvious implanted devices. If you see a medication patch where a pad belongs, remove it with a gloved hand or another barrier, wipe the area, and apply the pad. If the person has a visible pacemaker or implanted defibrillator, often seen as a small raised area under the skin near the upper chest, place the pad at least one inch away from it.

For an infant or child, use pediatric AED pads or a pediatric setting if the unit provides one. Pediatric pads reduce the energy level delivered. Follow the pad diagrams carefully, which may direct you to place one pad on the chest and one on the back if the pads could touch on a small child. If pediatric pads are unavailable, use adult pads if that is the only option, ensuring the pads do not touch each other.

Water requires judgment, not delay. Move the person away from standing water or a puddle if it can be done quickly and safely, then dry the chest before applying pads. Rain alone does not mean you should wait for an AED. In an oxygen-rich environment, move oxygen sources away from the chest area if possible, but do not disconnect oxygen from a patient if that action would create another risk or delay lifesaving care.

What “clear” really means

The most preventable AED error is allowing someone to touch the person during rhythm analysis or shock delivery. Touching the person can interfere with the AED’s rhythm reading, and contact during a shock can expose a rescuer to electrical energy.

Before analysis and before shock delivery, scan the entire scene. Make sure no one is touching the person, the stretcher, or the bed frame if it is connected to the person. Speak clearly and loudly. “Clear” is not a formality. It is a safety check that protects the team and gives the AED the best chance to assess the rhythm accurately.

Once the shock has been delivered or the AED advises “no shock,” restart chest compressions immediately. CPR remains essential because an AED does not restart every heart, and it does not replace circulation support between rhythm checks.

Continue until EMS takes over

Keep following the AED prompts and providing CPR until the person starts moving, breathing normally, or responding, or until EMS professionals take over. If the person begins breathing normally but remains unresponsive, place them on their side in a recovery position if there is no concern for trauma, monitor their breathing, and keep the AED pads attached. Cardiac arrest can recur, and the device may be needed again.

When EMS arrives, give a brief, organized handoff: when the person collapsed, whether the collapse was witnessed, when CPR started, how many shocks were delivered, and any known medical information. If the AED displays a time or event record, leave the pads and device in place for the responding team unless they direct otherwise.

Training makes the response faster

AEDs are built for public use, but hands-on practice matters. In a real emergency, people often lose time locating pads, managing clothing, or hesitating during the first analysis. CPR and AED training lets you rehearse those steps, practice effective compressions, and work through adult, child, and infant scenarios before the pressure is real.

For healthcare professionals, current BLS training helps align AED use with team roles, pulse checks, ventilation, and clinical response procedures. For parents, child-care providers, and community members, a CPR and First Aid course offers practical confidence without requiring a clinical background. HealthForce Training Center provides guided training pathways designed to fit busy schedules while helping learners complete required skills validation and credentials.

An AED cannot help if it stays on the wall. When seconds count, call 911, start CPR, turn on the device, follow its prompts, and keep going until help arrives. That calm, practiced sequence can give someone their best chance to survive.