Confirm unresponsiveness and absent normal breathing before anything else, then call 911, power on the AED, expose the bare chest, place electrode pads exactly as pictured, and follow each spoken prompt. The device decides whether a shock is needed and will never deliver one to a heart that does not require it. Modern AEDs are built so a panicked bystander can run the whole sequence with nothing but the voice in the speaker.
This practical walkthrough equips a panicked bystander with the confidence to run a defibrillator during a sudden cardiac emergency, covering scene assessment, pad placement, voice prompts, and safe shock delivery.
Recognizing a Cardiac Emergency and the Role of an AED
Sudden cardiac arrest (SCA) hits without warning, and the person collapses within seconds. The brain begins losing oxygen almost immediately, which is why the first few minutes matter more than any equipment that arrives later. Bystander action during that window is the single biggest factor in whether someone walks out of the hospital.
Unresponsiveness is the clearest signal. Tap the shoulder hard and shout. A person in cardiac arrest will not blink, moan, or flinch. Breathing also fails, but not always in the dramatic way movies suggest. The chest may rise in shallow, irregular gasps called agonal breathing, which looks like effort but does not move oxygen. Forget pulse-checking as a layperson. Even trained rescuers miss it under stress, and wasting minutes searching for one delays the two actions that matter.
Calling 911 and Sending for the AED
The moment you confirm collapse, shout for help and dial 911 yourself, or point at a specific bystander and tell them to call. Assign the AED task the same way. “You, in the blue shirt, find the AED on the wall and bring it back.” Specificity cuts through the bystander freeze that kills minutes.
An Automated External Defibrillator (AED) is a portable computer that reads heart rhythm through adhesive electrode pads and delivers a controlled electric shock. The shock briefly stops chaotic electrical activity so the heart’s natural pacemaker can restart in an organized rhythm. AEDs only shock ventricular fibrillation or pulseless ventricular tachycardia, two specific lethal rhythms where the heart quivers instead of pumping. If the rhythm is asystole (flatline) or another non-shockable pattern, the device refuses to fire.
Think of the AED as a referee. It watches the heart, decides if a penalty is warranted, and only calls one when the rules say so.
Preparing the Patient and the Scene Before Powering On
Scene safety comes before pad placement. A puddle of water on a gym floor or a metal bleacher can redirect the shock and endanger rescuers. Move the person onto a dry, non-metallic surface if you can do it in under ten seconds. Skip the move if it would take longer or risk a neck injury; speed beats perfection here.
Expose the Chest and Clear Obstacles
Clothing blocks the pads from skin, so cut or tear anything covering the torso open. A seatbelt cutter or the trauma shears tucked in most AED kits handles bra straps, sports bras, and thick jackets in one pass. Wipe away obvious sweat or pooled moisture, because wet skin spreads the shock across the chest instead of through the heart. Look for medication patches (nitroglycerin, hormone replacement, nicotine) on the skin, peel them off with a gloved hand or dry cloth, and wipe the residue away.
Metal jewelry near the collarbone or ribs can also redirect current. Pull off chains and large rings if doing so takes a second. Do not get distracted by belly button rings or toe rings; they sit too far from the pads to matter.
Dealing With Hair, Sweat, and Moisture
A chest thick with hair reduces pad adhesion and can create air pockets that weaken the shock. If a razor sits inside the AED case, shave only the two pad zones in quick strokes. If no razor is available, press the pads down firmly so the adhesive reaches the skin through the hair. A full chest shave wastes time; partial contact beats delayed shock every time.
Proper placement means nothing if the pads never make it onto the skin, so scene prep is the link between decision and delivery.
Warning: never place pads over a medication patch, a pacemaker bulge under the collarbone, or a wet surface. Shift at least one inch in any direction until the area is clean and dry.
Powering On the AED and Following Its Voice Prompts
Most AEDs activate the instant you open the lid or press a green power button. Some wall-mounted cabinets sound an alarm when you open them; that alarm is doing its job by scaring off anyone who might tamper with the device. Once on, the unit begins a calm audio script that walks you through every step in order. The script is recorded by people who understand that you are stressed, so the pace is slow and the sentences are short.
Listen, Watch, and Don’t Get Ahead
The pads ship in a sealed packet, often pre-connected to the cable. If yours are not, plug the connector into the port shown by a flashing icon. Peel the backing off each pad one at a time; the gel side is sticky and grabbing both at once wastes pads to the floor. Voice prompts and visual instructions on the pads and screen always show the same two locations on the chest, no matter the brand.
Trust the prompts exactly as they come. If the device says “attach pads,” it has already finished its self-test and is ready. If it says “analyzing rhythm, do not touch the patient,” stop moving and look at the chest. The repetition is intentional. People freeze, restart, or jump ahead under pressure, and the loop pulls them back on track.
Placing the Pads for Effective Electrical Delivery
Correct pad placement sends current straight through the heart muscle. Wrong placement sends it around the outside of the heart or through bone, which dilutes the shock. The standard adult position uses the upper right and lower left chest in what’s called the anterolateral placement.
Anterolateral Placement for Adults
The first pad sits on the upper right chest, just below the collarbone and right next to the breastbone. The second pad goes on the lower left side, a few inches below the armpit along the rib line, roughly at the level of the nipple. Picture a diagonal line running from shoulder to ribs, passing through the heart. Pads should lie flat with no bubbles, no folds, and no overlap.
Anterior-Posterior Placement for Children and Alternatives
Pediatric pads or the pediatric mode on a dual-setting AED typically call for anterior-posterior placement, since a child’s small chest cannot accommodate both pads in the standard spots without them touching. One pad goes on the center of the chest, the other on the center of the back between the shoulder blades. The diagram printed on pediatric pads shows this clearly; follow it even if it feels unfamiliar.
| Placement Type | Pad 1 Location | Pad 2 Location | Best For |
|---|---|---|---|
| Anterolateral | Upper right chest, below collarbone | Lower left ribs, below armpit | Most adults and children over 8 |
| Anterior-Posterior | Center of chest | Center of back, between shoulder blades | Small children, infants, atypical chests |
| Biaxillary (rare) | Right armpit line | Left armpit line | When standard sites are unusable |
Special cases come up in real life. On a woman with large breasts, lift the breast tissue and place the lower-left pad beneath it against the chest wall, rather than on top of the breast where contact is poor. On a person with a pacemaker bulge (a hard lump under the skin near the collarbone), place the pad at least one inch away from the device. On a person with a hairy chest, press hard once the pad sticks and let the gel do its work.
Analyzing the Rhythm, Standing Clear, and Delivering the Shock
The AED’s most important job is heart rhythm analysis, and it runs that analysis only when everyone is still. Announce loudly: “Everyone stand clear!” Make eye contact with each person in the room. Look down at the patient yourself and confirm no one is touching the chest, legs, or arms. Oxygen tubing, a metal stretcher rail, or even wet clothing touching the rescuer can all conduct current.
The Shock Itself
Some AEDs deliver a shock automatically when the rhythm calls for it. Others, including most public-access models, prompt you to press a flashing orange button. Press it only when the visual sweep of the room is complete. The shock lasts under a second, and the patient’s body may jerk visibly. That is normal muscle contraction, not a sign of damage.
When the AED Says No Shock
“No shock advised” means the heart is not in a rhythm the device can correct. The patient still needs help. Restart chest compressions immediately, because circulation matters even when the heart is not in a shockable state. The AED will reanalyze every two minutes, and a rhythm can flip back into something treatable during that window.
A shock is a reset, not a rescue, which is why compressions resume the moment the device clears the patient.
Pro tip: never silence the AED or unplug it to save time. Every pause in compressions drops survival odds, but every unnecessary delay in shock does too. Trust the sequence and keep your hands off when the device asks.
Resuming CPR, Coordinating Cycles, and Handing Off to EMS
Chest compressions buy time for the brain while the heart waits for the next chance to restart. Push hard and fast in the center of the chest, allowing full recoil between pushes. Cardiopulmonary resuscitation (CPR) at 100 to 120 compressions per minute lines up neatly with the beat of “Stayin’ Alive” if you need a metronome.
Coordinating Cycles With the AED
Compressions run for about two minutes, which is exactly how often the AED wants to reanalyze. Keep pauses under ten seconds when the device tells you to stand clear. When emergency medical services (EMS) arrive, the rhythm of your work shifts from solo to team. Paramedics will bring a manual monitor, IV access, and advanced airways, and they will want a quick handoff.
What to Tell Paramedics
Brief the lead paramedic on three things: the time you first applied the AED, the number of shocks delivered, and any change you saw in the patient’s color or breathing. If someone else took over compressions, mention that too. EMS crews document this history for the hospital, and it shapes what happens in the emergency room.
- Time of AED application: note the clock time or estimate from when 911 was called.
- Number of shocks: count them out loud during the event so you do not lose track.
- Patient changes: gasping stopped, color improved, eyes opened, anything visible.
- CPR duration: how long you or another bystander ran compressions before EMS arrived.
- Known history: heart condition, allergies, medications, or “none known” if you do not have it.
Training, Liability, and Why AEDs Are Safe for Untrained Users
AEDs are designed with layers of safety that prevent the worst outcomes a worried bystander fears. The device refuses to shock a non-shockable rhythm. It runs its own self-test every day and chirps if the battery is low or a pad is expired. It cannot deliver a shock to a person whose heart is beating normally, even if you press the button on purpose.
Legal Protection for Bystanders
Good Samaritan laws in every U.S. state and most Canadian provinces protect people who use an AED in good faith during a real emergency. The legal standard is reasonableness, not perfection. Skipping a step or pressing the wrong button once will not create liability if you were trying to help. Similar guidance covers the UK, where AEDs are increasingly common in railway stations and shopping centers.
Building Real Skill
Watching a video is not the same as feeling a manikin under your hands. Sign up for a certified course through the American Red Cross, American Heart Association, or an equivalent local provider. The session runs about four hours, costs less than a dinner out, and leaves you with a two-year certification. Many employers and community centers will reimburse the fee.
AEDs Are Already Everywhere
Federal and state regulations require AEDs in most federal buildings, many gyms, schools, and large workplaces. Walk into a shopping mall, airport, or hotel lobby and you will usually see one mounted on a wall near the elevator. Locate the nearest AED the next time you are in an unfamiliar building, the same way you would note an exit. That habit turns into seconds saved the day you actually need it.
Knowing the law and the training gap reframes every step above as something any bystander is legally and practically equipped to do.
Pro tip: download a phone app or check the mapping tool from your local EMS agency to find AEDs near your home and commute. Some communities maintain public registries that pinpoint devices on a map.
Bottom Line
A modern AED is built to coach you through the worst moment of your life, and the physics inside it are designed so that nothing you do halfway right will make things worse. Turn it on, follow the voice, place the pads where the diagram shows, stand clear when it analyzes, and resume compressions the instant it tells you to. The chain of survival depends on a bystander who acts before the ambulance arrives, and that bystander can absolutely be you.
FAQ
When should you use a defibrillator?
Apply a defibrillator to anyone who has collapsed and shows no normal breathing, because the device will analyze the rhythm and deliver a shock only when the pattern is treatable. Every minute of delay reduces survival odds, so power it on as soon as it arrives.
Do you need training to use an AED?
No certification is required to operate an AED in an emergency, and Good Samaritan laws protect bystanders who act in good faith. A short CPR and AED course through the American Red Cross or American Heart Association builds muscle memory and confidence for real events.
Where do you place AED pads on a person?
Standard adult placement puts one pad on the upper right chest below the collarbone and the other on the lower left side below the armpit. Pediatric or small-chest situations use anterior-posterior placement with one pad on the chest and one on the back.
Can a defibrillator restart a stopped heart?
An AED cannot restart a heart that is in asystole, also called flatline. It only corrects ventricular fibrillation and pulseless ventricular tachycardia by depolarizing the heart muscle so the natural pacemaker can resume an organized rhythm.
Is it safe to use a defibrillator on a child?
Yes, with pediatric pads or a pediatric-mode setting for children under eight. Place pads in the anterior-posterior position if chest size prevents the standard anterolateral layout, and follow the diagrams printed on the pads.
What do you do after using a defibrillator?
Resume chest compressions immediately after any shock, continue until the AED reanalyzes or the patient shows signs of life, and hand off to EMS with the time of application, number of shocks, and any visible changes. Replace used pads and report the event so the device can be serviced and returned to service.
