Using an AED (automated external defibrillator) comes down to three actions: turn it on, stick the pads on the person’s bare chest, and follow the voice prompts. The device does the hard part for you. It analyzes the heart rhythm, decides whether a shock is needed, and tells you exactly what to do at each step. You do not need training or certification to use one.
When To Use an AED
An AED is for one situation: sudden cardiac arrest. That means the person’s heart has stopped pumping blood effectively. The signs are unmistakable. The person collapses suddenly, loses consciousness, and isn’t breathing normally (or isn’t breathing at all). This is different from a heart attack, where someone typically stays conscious and complains of chest pain. Cardiac arrest is an electrical malfunction in the heart, and an AED exists to fix that malfunction with a controlled shock.
If someone is unconscious, unresponsive, and not breathing, treat it as cardiac arrest. Have someone call 911 immediately and start CPR while another person grabs the nearest AED. Every minute without treatment reduces the chance of survival, so speed matters more than perfection.
Step-by-Step: Operating the AED
1. Turn It On
Open the case and press the power button, or simply open the lid (some models activate automatically). The device will begin speaking to you with clear voice prompts. Listen and follow along. Every AED on the market is designed to walk an untrained bystander through the process.
2. Expose the Chest and Attach the Pads
Remove all clothing covering the person’s chest. If the skin is wet from sweat, rain, or water, wipe it dry first. Most AED kits include a small towel for this. Moisture reduces how well the pads stick and can interfere with shock delivery.
Peel the backing off the adhesive pads and place them on bare skin:
- Pad one: upper right chest, just below the collarbone
- Pad two: lower left side, a few inches below the left armpit
The pads themselves have diagrams showing exactly where they go. If the connector cable isn’t already attached to the AED, plug it in.
3. Let the AED Analyze
The device will tell you to stop touching the person so it can analyze the heart rhythm. Say “CLEAR!” loudly so that everyone nearby steps back. Even small movements or contact can interfere with the reading. Keep your hands off the person and make sure nobody else is touching them either.
4. Deliver the Shock (If Prompted)
If the AED detects a rhythm that can be corrected with a shock, it will tell you to press the shock button. Say “CLEAR!” again, confirm no one is touching the person, and press the button. Some fully automatic models deliver the shock without requiring you to press anything, but most public-access AEDs require that button press as a safety step.
If the AED determines no shock is needed, it will tell you. This doesn’t mean you did something wrong. It means the heart rhythm isn’t the type that responds to defibrillation. Continue CPR.
5. Resume CPR Immediately
Right after the shock (or after a “no shock advised” message), start CPR again. Push hard and fast in the center of the chest, aiming for about 100 to 120 compressions per minute. Continue for 2 minutes. The AED will prompt you when it’s time to pause and reanalyze the rhythm. Keep cycling between CPR and AED analysis until emergency medical services arrive or the person starts breathing and moving.
Leave the pads attached even if the person regains consciousness. The heart can slip back into a dangerous rhythm, and the AED needs to stay ready.
Handling Common Complications
A few situations require a quick extra step before you attach the pads. AED kits typically include supplies for all of these.
Excessive chest hair. If thick hair prevents the pads from making good contact with the skin, shave the area first. Most kits include a small razor. Press the pads down firmly after shaving.
Medication patches. If there’s a nicotine patch, pain patch, or any other medicated patch on the chest where a pad needs to go, peel it off and wipe away any residue. Leaving a patch under an AED pad can cause burns when the shock is delivered.
Implanted pacemaker or defibrillator. You can usually see or feel a small hard lump under the skin, typically below the collarbone. Don’t place a pad directly over it. Position the pad at least four finger-widths away from the device.
Wet environment. Move the person to a dry surface if possible. You don’t need to move them far, just out of standing water. Dry the chest before applying pads. An AED can be used in rain as long as the chest is wiped dry and the person isn’t lying in a puddle.
Using an AED on Children
For children aged 8 and older (or weighing more than 55 pounds), use the standard adult pads and follow the same steps described above. For younger or smaller children, use pediatric pads if the AED kit includes them. These deliver a lower energy dose. If pediatric pads aren’t available, adult pads are still safe to use.
One important difference with small children: if the two pads are large enough that they might touch each other on the chest, place one pad on the center of the chest and the other on the back between the shoulder blades. This front-and-back positioning still allows the electrical current to pass through the heart.
You’re Legally Protected
A common fear is being sued for using an AED incorrectly. Federal law addresses this directly. The Cardiac Arrest Survival Act of 2000 grants civil immunity to any person who uses or attempts to use an AED on someone experiencing a perceived medical emergency. This protection applies as long as you’re acting in good faith and without gross negligence or willful misconduct. Nearly every state has its own Good Samaritan law that reinforces this protection.
In practical terms, this means you cannot be held liable for trying to save someone’s life with an AED, even if the outcome isn’t good. The legal system recognizes that bystander intervention during cardiac arrest is overwhelmingly beneficial, and the law is designed to remove hesitation. The far greater risk is doing nothing. Without defibrillation, fewer than 10% of people who experience cardiac arrest outside a hospital survive.
What the AED Does That You Can’t
The most important thing to understand is that an AED will not let you shock someone who doesn’t need it. The device analyzes the heart’s electrical activity and only enables the shock button when it detects ventricular fibrillation or ventricular tachycardia, the two chaotic heart rhythms that respond to defibrillation. If the heart is in any other state, the AED simply won’t allow a shock to be delivered. This built-in safeguard means you cannot accidentally harm someone by using the device. The technology makes the medical decision. You just follow the prompts.