How to Use an AED: A Step-by-Step Guide to Restart a Heart in an Emergency

When someone collapses and does not respond, every second matters. An automated external defibrillator (AED) can analyze the heart's rhythm and deliver an electric shock when appropriate. Used together with CPR, an AED may help restore an effective heart rhythm while emergency medical services are on the way.

The good news is that AEDs are designed for everyday people, not just healthcare professionals. The device provides voice and visual instructions to guide you through the process. Still, knowing the basic steps before an emergency happens can make it easier to respond with confidence.

This guide follows the general sequence taught in American Red Cross CPR/AED programs and HSI CPR, AED, and first aid training. Always follow the instructions from the AED in front of you and directions from the 911 dispatcher.

Important: This article is for general education and does not replace hands-on CPR/AED training. If a person is unresponsive and not breathing normally, call 911 immediately and begin CPR.

What Is an AED?

An AED is a portable medical device that analyzes a person's heart rhythm. If it detects a shockable rhythm associated with sudden cardiac arrest, it instructs the rescuer to deliver a shock.

An AED does not shock every person who collapses. It evaluates the rhythm and will tell you either “shock advised” or “no shock advised.” You cannot accidentally deliver a shock simply by placing the pads on the person and following the prompts.

An AED may be found in schools, offices, gyms, airports, churches, community centers, healthcare facilities, and other public locations. Knowing where the nearest AED is located should be part of every workplace or organization's emergency plan.

Before Using an AED: Recognize Cardiac Arrest

Use an AED when an adult is:

• Unresponsive or does not respond when you tap their shoulders and speak loudly
• Not breathing normally
• Only gasping, making irregular snorting sounds, or taking occasional breaths

Gasping is not normal breathing. Treat it as a sign of cardiac arrest.

Before approaching, quickly check that the scene is safe. Do not enter an area with active electrical hazards, fire, traffic, violence, or other dangers. If the scene is safe, take standard precautions such as using gloves or a breathing barrier if available.

Step 1: Call 911 and Send Someone for the AED

If the person is unresponsive, call 911 or direct someone specific to make the call.

Use clear instructions:

• “You in the blue shirt, call 911.”
• “You, get the AED.”
• “Meet the ambulance at the entrance.”

If you are alone with an adult, call 911 first, preferably using speakerphone, then begin CPR and retrieve or use the AED as soon as possible. The dispatcher may be able to guide you through the initial steps.

If other people are present, one person should call 911, one should bring the AED, and another should begin CPR.

Step 2: Start CPR While the AED Is Being Retrieved

Place the person on their back on a firm, flat surface. Kneel beside the chest and place both hands in the center of the chest, on the lower half of the breastbone.

Begin chest compressions:

• Push hard and fast at a rate of 100 to 120 compressions per minute.
• Allow the chest to fully recoil after every compression.
• Minimize interruptions.

If trained and willing, provide cycles of 30 compressions followed by 2 rescue breaths. If you are not trained, are uncomfortable giving breaths, or do not have a barrier device, provide continuous chest compressions.

Continue CPR until the AED arrives or another trained rescuer takes over.

Step 3: Turn On the AED

As soon as the AED arrives, turn it on. Depending on the model, you may need to press a power button or open the lid.

Listen carefully to the voice prompts and look at the diagrams. AEDs are designed to guide rescuers step by step, so do not worry if the device looks unfamiliar.

If another rescuer is providing CPR, tell them to continue compressions while you prepare the AED. When the device tells everyone to stop, pause CPR and allow it to analyze the rhythm.

Step 4: Expose and Prepare the Chest

Remove or cut away clothing covering the chest. AED pads must stick directly to bare skin.

If the chest is wet, quickly dry it with a towel, clothing, or gauze. Do not apply pads over wet skin if you can safely dry the area first.

Check the chest for anything that could interfere with pad placement:

• Do not place a pad directly over a visible medication patch. Remove the patch with a gloved hand if necessary and wipe away any medication.
• If the person has an implanted pacemaker or defibrillator, avoid placing a pad directly over the raised device. Place the pad beside it according to the AED diagram.
• Do not delay lifesaving care trying to shave chest hair unless the pads will not adhere and a razor is immediately available.

Step 5: Apply the AED Pads

Peel the backing from the adhesive pads. Avoid touching the sticky surfaces more than necessary.

For most adults:

• Place one pad on the upper right side of the chest, just below the right collarbone.
• Place the second pad on the lower left side of the chest, below the left armpit and toward the side of the rib cage.

Use the pictures printed on the pads as your guide. Press each pad firmly against the skin so it adheres completely.

If the person has a very small chest and the pads could touch each other, place one pad on the front of the chest and the other on the back between the shoulder blades. Follow the AED's instructions whenever possible.

Connect the pad cable to the AED if it is not already connected.

Step 6: Let the AED Analyze the Heart Rhythm

When the AED says it is analyzing, nobody should touch the person.

Announce loudly, “Everybody clear!” Then look around the person to make sure no one is touching the body, clothing, stretcher, or other connected equipment.

Touching the person during analysis can interfere with the device's ability to read the rhythm accurately. Wait for the AED to provide its next instruction.

Step 7: Deliver a Shock If the AED Advises One

If the AED says “shock advised,” make sure everyone is clear again.

Say, “Everybody clear!” Look carefully to confirm that nobody is touching the person. If the device requires you to press a shock button, press it when instructed. Some AEDs deliver the shock automatically.

Do not touch the person during the shock. The shock may cause the body to jerk — this is expected. Do not remove the pads or turn off the AED after the shock.

Step 8: Resume CPR Immediately

As soon as the shock is delivered, or if the AED says “no shock advised,” resume CPR immediately, beginning with chest compressions.

The AED will typically reanalyze the heart rhythm after a period of CPR, often about two minutes. Follow its prompts each time:

• Perform CPR.
• Stop when the AED says it is analyzing.
• Clear the person.
• Deliver a shock if advised.
• Resume CPR immediately.

Continue this cycle until emergency medical services take over, another trained responder replaces you, or the person shows clear signs of life.

What If the Person Is a Child or Infant?

Use pediatric AED pads or a pediatric setting when available and appropriate for the child's age and size. Follow the device instructions.

If pediatric pads are not available, many AEDs can be used with adult pads. Make sure the pads do not touch each other. For a small child or infant, front-and-back placement may be necessary.

Pediatric CPR and AED use have specific considerations, which is why parents, caregivers, teachers, daycare staff, coaches, and healthcare professionals benefit from hands-on training that covers adults, children, and infants.

Common AED Questions

Can an untrained person use an AED?

Yes. AEDs are designed to guide the rescuer with voice prompts, lights, and diagrams. If someone collapses and appears to be in cardiac arrest, do not wait for a certified responder before beginning CPR or using an AED.

Can an AED hurt someone who is not in cardiac arrest?

The AED analyzes the heart rhythm before recommending a shock. Follow the device prompts and do not touch the person during analysis or shock delivery.

Should I remove the AED pads after the person wakes up?

No. Leave the pads in place and keep the AED turned on. Continue following the device's instructions and monitor the person until EMS arrives.

What if the AED says “no shock advised”?

Resume CPR immediately. A shock is not appropriate for every cardiac rhythm, but CPR can continue providing circulation while you wait for professional care.

Build Confidence Before an Emergency

Reading about AED use is helpful, but hands-on practice makes the steps easier to remember under pressure. I offer mobile First Aid, CPR & AED training for individuals, families, schools, offices, fitness centers, childcare programs, healthcare teams, and community organizations throughout Southern California.

Training is available through Red Cross and HSI programs, with flexible classroom and blended-learning options. Practical sessions let participants practice chest compressions, AED pad placement, rhythm analysis, and coordinated response using training equipment.

I come to you — providing mobile training throughout San Diego County, Temecula, Murrieta, Menifee, and Lake Elsinore.

Training is by appointment only. To request a class, contact Code Blue Safety Skills by email or call (951) 669-4177. Please include the specific dates you want for the class, along with your preferred location, course type, and estimated group size.

Knowing how to call for help, begin CPR, and use an AED can turn a frightening emergency into an organized response. Training helps ensure you are ready to act when every second counts.