Using an AED is straightforward: you turn it on, attach two sticky pads to the person’s bare chest, and let the machine decide whether to deliver a shock. Every AED walks you through the process with voice prompts, so you don’t need medical training to operate one. When someone collapses in cardiac arrest, rapid defibrillation can improve their survival rate by more than 50%, and every minute without it reduces their chances significantly.
Before You Touch the AED
If someone collapses and isn’t breathing normally, call 911 (or have someone else call) and start chest compressions immediately. Push hard and fast in the center of the chest, about 100 to 120 compressions per minute. Send someone to grab the nearest AED while you keep compressions going. The goal is to minimize any gap between compressions and the first shock.
Once the AED arrives, place it next to the person’s head or torso so the electrode cables can reach the chest easily. Don’t stop CPR until the machine tells you to.
Step-by-Step AED Use
Open the case and press the power button. Some models turn on automatically when you open the lid. The machine will immediately begin giving you voice instructions. Follow them exactly, even if you’ve used an AED before, because timing matters and the prompts keep you on track.
Expose the person’s bare chest. Cut or tear clothing away if needed. Then peel the backing off the electrode pads and stick them to the skin in the positions shown on the diagrams printed on the pads themselves. For adults and children eight and older, one pad goes below the right collarbone, just to the right of the breastbone. The other goes on the left side of the chest, below the armpit on the mid-axillary line. Make sure the pads don’t incorporate any breast tissue.
For children under eight, if pediatric pads are available, place one on the front of the chest over the heart and one on the back, just below the left shoulder blade. If you only have adult pads, you can use them on a child or infant as long as the two pads don’t touch each other.
Once the pads are attached, the AED analyzes the heart’s rhythm automatically. It will tell everyone to “stand clear.” Make sure nobody is touching the person during analysis. If the machine detects a rhythm that can be corrected with a shock, it will charge up and tell you to press the shock button. Some fully automatic models deliver the shock without you pressing anything. After the shock (or if no shock is advised), the AED will prompt you to resume CPR for two minutes before it analyzes again.
Preparing the Chest for Pad Contact
The pads need direct, firm contact with dry skin to work properly. Several common situations can interfere with that contact, and most AED kits come prepared for them.
If the person’s chest is wet from rain, sweat, or water, dry it thoroughly with a towel or cloth before applying the pads. If they’re lying in a puddle or pool, move them to a dry surface first. Water conducts electricity and could create a pathway for the shock to reach you or bystanders.
A very hairy chest can trap air under the pads and prevent good contact. Most AED kits include a small razor. Quickly shave the areas where the pads will go. If there’s no razor, press the pads down as firmly as you can to compress the hair against the skin.
If you see a medication patch (nitroglycerin patches are common), peel it off and wipe the residue from the skin before placing a pad in that spot. Leaving a patch in place can cause a burn.
Pacemakers and Implanted Devices
You may notice a hard lump under the skin of the upper chest, typically below the collarbone. That’s likely a pacemaker or implanted defibrillator. Don’t place a pad directly over it, as this reduces how well the shock works. Instead, position the pad at least one inch (about 2.5 cm) away from the device and continue as normal.
If the person has an implanted defibrillator that’s already firing (you’ll see their muscles contract rhythmically, similar to what external defibrillation looks like), give the device 30 to 60 seconds to complete its cycle. If the person is still unresponsive after that, attach the AED and follow the prompts.
What the Machine Does for You
Modern AEDs are designed so that someone with zero training can use them successfully. The voice prompts guide every step, from pad placement to shock delivery. Many devices also include a metronome that beeps at the correct compression rate (100 beats per minute) so you can keep rhythm during CPR between shocks. Some models add visual signals, like flashing lights, to reinforce the audio cues.
Critically, the AED decides whether a shock is appropriate. You cannot accidentally shock someone who doesn’t need it. The machine analyzes the heart rhythm and will only charge if it detects a pattern that defibrillation can correct. If the rhythm isn’t shockable, it will tell you “no shock advised” and prompt you to continue CPR.
Why Speed Matters
Data from real-world cardiac arrests shows that people who receive an AED shock within five minutes have a one-month survival rate of about 35%. Between five and ten minutes, that rate holds relatively steady at around 37%. But beyond ten minutes, survival drops to about 28%. The difference between acting quickly and waiting for paramedics can be the difference between someone walking out of a hospital and not surviving at all.
AEDs are now installed in airports, gyms, schools, office buildings, shopping centers, and many other public spaces, often in wall-mounted cabinets marked with a green heart symbol. Knowing where the nearest one is before an emergency happens gives you a meaningful head start.
Legal Protection for Bystanders
Every U.S. state has some form of Good Samaritan law that protects people who use an AED in good faith during an emergency. These laws generally mean you cannot be held liable for civil damages as long as you acted reasonably and without gross negligence. In practical terms, if you see someone in cardiac arrest and grab the nearest AED, the law is on your side. The legal system recognizes that a bystander trying to help is far better than a bystander doing nothing.
Metal Surfaces and Other Concerns
A common worry is whether using an AED on a metal surface, like a bleacher or industrial floor, could shock bystanders. It won’t. Metal surfaces do not create a shock hazard for the rescuer or the person being treated. The only environmental concern that requires action is water, which you should address by moving the person to a dry area and drying their chest before applying pads.