You should use an AED any time someone collapses, is unresponsive, has no pulse, and is not breathing normally. These are the signs of sudden cardiac arrest, and every minute without defibrillation reduces the chance of survival by 7 to 10%. The device itself will analyze the heart rhythm and decide whether a shock is needed, so your job is simply to turn it on and follow its voice prompts.
Recognizing Sudden Cardiac Arrest
Sudden cardiac arrest looks dramatic and unmistakable. The person collapses without warning, doesn’t respond when you tap their shoulders and shout, and either isn’t breathing at all or is only gasping irregularly. Those gasps (sometimes called agonal breathing) can fool bystanders into thinking the person is still breathing normally. They’re not. Gasping without consciousness counts as not breathing.
The moment you confirm someone is unresponsive and not breathing normally, call 911 (or have someone nearby do it), start chest compressions, and send someone to grab the nearest AED. Speed matters more than perfection here. The heart is likely in a chaotic electrical state where it quivers instead of pumping blood. An AED delivers a controlled shock that can reset that rhythm, but only if it arrives quickly.
How the AED Decides Whether to Shock
An AED doesn’t shock every heart it analyzes. It’s programmed to recognize two specific rhythms: ventricular fibrillation, where the heart’s electrical signals are completely disorganized, and pulseless ventricular tachycardia, where the heart beats dangerously fast without effectively pumping blood. These are the only two “shockable” rhythms in cardiac arrest.
If the AED detects either one, it will charge and instruct you to press the shock button (or, in fully automatic models, deliver the shock on its own). If the heart has stopped entirely or is in a rhythm that a shock won’t fix, the AED will announce “no shock advised” and tell you to continue CPR. You cannot accidentally shock someone who doesn’t need it. The device makes that call for you.
Step-by-Step: Using an AED
Turn the AED on and follow the voice prompts. Every model walks you through the process out loud, but here’s what to expect:
- Expose the chest. Remove or cut away clothing so the pads make direct skin contact. If the chest is wet, wipe it dry quickly. If there’s excessive chest hair preventing the pads from sticking, use the razor included in most AED kits to shave the pad areas.
- Peel and place the pads. One pad goes on the upper right chest, below the collarbone. The other goes on the lower left side, under the armpit. The pads themselves have diagrams showing exactly where they go.
- Stand clear during analysis. The AED will tell everyone to stop touching the person while it reads the heart rhythm. Any movement can interfere with the reading.
- Deliver the shock if prompted. Make sure no one is touching the person, then press the shock button.
- Resume CPR immediately. Whether the AED delivers a shock or advises against one, start chest compressions right away. Continue for two minutes until the AED prompts you to pause for another rhythm check.
This cycle of analyze, shock (if indicated), and two minutes of CPR repeats until emergency medical services arrive or the person starts breathing and moving on their own.
Using an AED on Children
AEDs can be used on children and infants. For children under 8 years old, use pediatric pads or a pediatric dose attenuator if the AED has one. These deliver a lower energy shock appropriate for a smaller body. If pediatric pads aren’t available, use the standard adult pads and adult shock dose. A shock at adult energy is far better than no shock at all.
One important rule works in reverse: never use pediatric pads on an adult. The reduced energy dose is too low to be effective on an adult-sized heart.
Medication Patches and Pacemakers
If the person has a medication patch (such as a nitroglycerin patch) where you need to place a pad, peel it off and wipe the skin dry before attaching the electrode. Don’t touch the patch with bare hands, as the medication can absorb through your skin. Use the gloves found in most AED kits.
If you notice a visible lump under the skin on the upper chest, that’s likely an implanted pacemaker or defibrillator. You can still use the AED. Place the pad at least one inch (about 2.5 cm) away from the device. If the implant is right where a pad would normally go, shift the pad to the nearest acceptable position that avoids it. The AED will still work effectively.
Wet Surfaces and Metal Floors
A common concern is whether AEDs are safe to use around water or on metal surfaces like a boat deck, a factory floor, or poolside concrete. Current research and AED manufacturers confirm that modern AEDs are self-grounded, meaning they can be safely used in wet environments with minimal risk to the rescuer or bystanders. A bystander on the same wet or metal surface might feel a slight tingle at most during the shock, but nothing dangerous.
The key precautions are straightforward: dry the person’s chest so the pads stick properly and make good electrical contact, and make sure you’re not physically touching the person’s chest when the shock is delivered. You don’t need to move the person to a dry surface before starting. That delay could cost critical minutes.
Why Speed Matters More Than Expertise
Survival from cardiac arrest drops roughly 7 to 10% with every passing minute of an untreated shockable rhythm. At that rate, a person’s odds fall below 50% within about five minutes. Emergency medical services take an average of 8 to 12 minutes to arrive in most areas, which is why bystander action with an AED is so critical. People who receive defibrillation within the first few minutes of cardiac arrest have dramatically better outcomes than those who wait for paramedics.
The AED is designed so that anyone can use it with zero training. You cannot shock someone who doesn’t need it, you cannot deliver the shock at the wrong time (the device controls the timing), and the voice prompts guide every step. If you’re standing near someone in cardiac arrest and there’s an AED on the wall, grab it. There is no scenario where attempting to use it makes things worse.