Using an AED (automated external defibrillator) comes down to turning it on, placing two adhesive pads on the person’s bare chest, and letting the device tell you what to do next. The machine analyzes the heart rhythm automatically and will only deliver a shock if one is needed. You do not need medical training to operate one, and the voice prompts guide you through every step.
What an AED Actually Does
When someone collapses in cardiac arrest, their heart is often in one of two dangerous rhythms: ventricular fibrillation, where the heart quivers chaotically instead of pumping, or pulseless ventricular tachycardia, where it beats so fast it can’t move blood. Neither produces a pulse. The AED delivers a controlled electrical shock that simultaneously resets the heart’s electrical activity, essentially hitting pause so the heart’s natural pacemaker can restart a coordinated rhythm and restore a pulse.
An AED will not shock a heart that has flatlined or one that is beating normally. The device analyzes the rhythm first and only allows a shock for those two specific patterns. This means you cannot accidentally shock someone who doesn’t need it.
Step-by-Step: Using an AED
Before you touch the AED, confirm the person is unresponsive and not breathing normally. Call 911 (or have someone else call), then begin chest compressions. If an AED is nearby, send someone to grab it while you keep doing compressions. Every second without blood flow matters.
Turn It On and Follow the Prompts
Open the case and press the power button, or simply open the lid if the device activates automatically. A voice will begin giving instructions immediately. Remove or cut away clothing to expose the person’s bare chest. The adhesive pads have diagrams printed on them showing exactly where to place each one: one pad goes on the upper right chest, just below the collarbone, and the other goes on the lower left side of the chest, below the armpit. Peel the backing off and press them firmly against the skin.
Let the AED Analyze
Once the pads are attached, the device will tell everyone to stand clear while it reads the heart rhythm. Stop chest compressions and make sure nobody is touching the person. Do not move the patient during analysis. The AED needs a still reading to determine whether a shock is appropriate.
Deliver the Shock (If Advised)
If the AED detects a shockable rhythm, it will charge and instruct you to press the shock button. Some fully automatic models deliver the shock without requiring a button press. Before shocking, look around and loudly say “Clear!” to confirm no one is in contact with the person. Press the button when prompted.
Resume CPR Immediately
Right after the shock, start chest compressions again at a rate of about 100 per minute. Do not wait to see if the person wakes up. Continue compressions for two minutes (roughly 200 compressions), then the AED will automatically begin another rhythm analysis. Repeat this cycle of analyze, shock if advised, and compress for two minutes until paramedics arrive or the person starts breathing and moving on their own.
If the AED says “no shock advised,” that does not mean the person is fine. It means the heart rhythm isn’t one a shock can fix. Continue chest compressions and let the AED re-analyze every two minutes.
Pad Placement for Children
For children under 8 or weighing less than 55 pounds, use pediatric pads if the AED has them. These deliver a lower energy dose. If pediatric pads aren’t available, use the adult pads. On a small chest where the pads might overlap, place one on the center of the chest and one on the center of the back. The AED voice prompts will often walk you through this as well.
Safety Precautions
A few environmental factors matter. If the person is lying in a puddle or pool of water, drag them to a dry surface before attaching the pads. Using an AED in rain or snow is safe. Metal surfaces like a factory floor or bleachers are also safe, but make sure the pads aren’t directly touching the metal and that no one is in contact with the person when the shock fires.
For clothing and accessories: remove the person’s bra or move it out of the way so pads make full contact with skin. Don’t place pads directly over metallic jewelry or piercings, but don’t waste time removing them either. Just position the pads slightly off to one side. Chest hair rarely causes a problem with pad adhesion, so shaving is almost never necessary. If pads genuinely won’t stick because of very thick hair, some AED kits include a razor, but speed matters more than a perfect chest prep.
If the person has a medication patch on their chest where a pad needs to go, peel it off and wipe the area before placing the pad. Implanted pacemakers or defibrillators create a visible bump under the skin, usually below the collarbone. Avoid placing a pad directly over that bump; shift it a few inches to one side.
You’re Legally Protected
Every U.S. state has some form of Good Samaritan law that protects people who provide emergency care in good faith. In California, for example, state law explicitly shields lay rescuers from civil liability when using an AED, as long as the device has been maintained according to manufacturer guidelines. The legal framework exists specifically to encourage bystanders to act. You face far greater moral risk by doing nothing than legal risk by trying to help.
Keeping an AED Ready
If you’re responsible for an AED at a workplace, gym, or community center, maintenance is straightforward but essential. Electrode pads typically expire after about two years. Batteries last two to five years depending on the model. Most modern AEDs run daily self-checks and display a green indicator light when everything is functional. Check that light regularly, and replace pads and batteries before their expiration dates. An AED with dead batteries or dried-out pads is just a plastic box.
Keep a log of inspection dates and any use. Some state regulations require reporting the AED’s location to local emergency medical services, which helps dispatchers direct 911 callers to the nearest device.
Why Speed Is Everything
For every minute that passes without defibrillation during cardiac arrest, the chance of survival drops roughly 7 to 10 percent. Brain damage begins within four to six minutes without blood flow. Paramedic response times average eight to twelve minutes in most areas. That gap is why public-access AEDs exist, and why bystander action is the single biggest factor in whether someone survives cardiac arrest outside a hospital. The device does the hard thinking. Your job is to turn it on, stick the pads where the pictures show, and follow the voice.