What Are the 7 Steps of Using an AED?

The seven steps of using an automated external defibrillator follow a straightforward sequence: check the person for responsiveness, call emergency services, power on the AED, expose the chest and attach the electrode pads, let the device analyze the heart rhythm, deliver a shock if the AED advises one, and immediately resume CPR. Every modern AED walks you through this process with voice prompts, and the whole sequence from opening the case to delivering a shock can take under a minute when things go smoothly. But understanding what each step accomplishes and where people commonly stumble makes a real difference, because time during cardiac arrest is brutally unforgiving.

Why Every Minute Counts

Sudden cardiac arrest kills quickly. Without intervention, survival drops from roughly half when defibrillation happens almost immediately to around 5% when it is delayed 15 minutes.¹ A large analysis of witnessed cardiac arrests found that every additional minute of delay was associated with a 6% lower chance of surviving to hospital discharge.² That same minute of delay also reduced the odds of the heart returning to an organized rhythm. These numbers explain why AEDs are designed the way they are: simple enough that an untrained person can use one, with voice guidance that eliminates the need to make medical decisions on the spot.

When bystanders apply an AED before paramedics arrive, the odds of survival roughly double compared with waiting for emergency medical services alone. A study across a population base of 21 million people found that bystander AED use before EMS arrival was associated with about 75% higher odds of survival.³ A systematic review of public-access defibrillation programs reported a median survival to hospital discharge of about 40% when an AED was used by bystanders, with lay first responders achieving survival rates as high as 53%.⁴

Step by Step Through the Process

Step 1: Check for Responsiveness

Before you do anything else, make sure the scene is safe and confirm the person is actually unresponsive. Tap their shoulders firmly and shout. If they do not respond, are not breathing normally, or are only gasping, you are looking at a potential cardiac arrest. Do not spend more than a few seconds on this assessment. The goal is to confirm the person needs help, not to diagnose what happened.

Step 2: Call Emergency Services and Send for the AED

Call 911 (or your local emergency number) immediately. If other people are nearby, point at someone specific and tell them to call while you start helping. Point at a second person and send them to find the nearest AED. Many public buildings, airports, gyms, and offices have AEDs in clearly marked cabinets. If you are alone, put your phone on speaker, call emergency services, and begin CPR. Some dispatch centers can now guide bystanders to the nearest AED location. Programs that have dispatchers direct callers to retrieve nearby AEDs have increased the rate of public AED use from about 5% to nearly 9% of eligible cardiac arrest cases.⁵

Step 3: Power On the AED

Open the case and press the power button, or simply open the lid if the device turns on automatically. The AED will begin giving you voice instructions. Follow them. These devices are designed so that a person who has never seen one before can use it successfully. Some AEDs also have visual prompts on a screen or indicator lights that walk you through each action.

Step 4: Expose the Chest and Attach the Pads

Remove or cut away clothing from the person’s chest. The pads need to make direct contact with bare, dry skin. Each pad has a diagram showing where it goes: one on the upper right chest below the collarbone, and the other on the lower left side under the armpit. Peel the backing off and press them firmly into place. If the person’s chest is wet, wipe it dry first. If there is excessive chest hair preventing a good seal, some AED kits include a razor for this purpose.

Step 5: Let the AED Analyze the Rhythm

Once the pads are connected, the AED will tell everyone to stand clear while it analyzes the heart rhythm. Do not touch the person during this phase. The device is reading the electrical activity of the heart to determine whether a shock could help. If the rhythm is shockable (typically ventricular fibrillation or pulseless ventricular tachycardia), the AED will charge and tell you to press the shock button. If the rhythm is not shockable, it will tell you no shock is advised and prompt you to continue CPR.

Step 6: Deliver the Shock

If the AED says “shock advised,” make sure nobody is touching the person. Say “clear” out loud, visually confirm no one is in contact, and press the flashing shock button. The person’s body may jerk slightly. This is the moment the device delivers an electrical pulse designed to reset the heart’s chaotic electrical activity. Fully automatic AEDs (less common) deliver the shock without you pressing a button, but will still warn you to stand clear first.

Step 7: Immediately Resume CPR

Right after the shock, begin chest compressions without pausing to check for a pulse. This is the step people often get wrong. The instinct is to wait and see if the shock worked, but the heart frequently needs several minutes of compressions after a successful shock before it can pump blood effectively on its own. Current guidelines call for two minutes of CPR before the AED re-analyzes the rhythm.⁶ The AED will time this for you and prompt you when it is ready to analyze again. Leave the pads in place; the cycle of CPR, analysis, and possible additional shocks continues until paramedics take over or the person starts breathing and moving.

Where Pad Placement Goes Wrong

Getting the pads in the right spot matters more than people realize. A study examining how well rescuers follow the diagrams printed on AED pads found that the upper chest pad was generally placed close to optimal, but the lower pad (the one that goes under the left armpit) was placed an average of about 78 mm too low and 59 mm too far toward the center of the chest.⁷ That lower pad should sit on the left side of the ribcage, roughly at the level of the bottom of the person’s armpit, not down near the waist. The diagrams on the pads themselves are your best guide, but be aware the tendency is to place that second pad too low and too centered.

For children between one and eight years old, use pediatric pads if available. These deliver a lower energy dose. If no pediatric pads are in the kit, use adult pads. If the child is small enough that the pads might touch or overlap on the chest, place one pad on the front of the chest and the other on the back. For infants under one year, manual defibrillation by trained medical personnel is preferred, but an AED with pediatric pads is still better than doing nothing.

How the AED Decides Whether to Shock

The analysis algorithm inside an AED is doing something genuinely sophisticated. It reads the electrical signal from the heart through those adhesive pads and classifies the rhythm as shockable or non-shockable. A shock only helps when the heart is in certain chaotic rhythms. If the heart has stopped producing any electrical activity at all (asystole, or “flatline”), a shock will not restart it. This is the opposite of what television and movies show.

Modern AED algorithms are highly accurate. One study of a neural-network-based algorithm found it classified shockable rhythms with 98% sensitivity and 100% specificity.⁸ In pediatric cardiac arrests, the sensitivity was somewhat lower at about 89%, with specificity near 100%.⁹ That high specificity is the critical number for bystanders to understand: it means the device almost never advises a shock when one is not needed. You can trust the AED’s judgment. If it says shock, shock. If it says no shock, do CPR.

Newer algorithms can even analyze the rhythm during chest compressions, classifying the signal as shockable, non-shockable, or flagging that a pause is needed for clearer reading.¹⁰ This matters because every pause in CPR reduces blood flow to the brain and heart, so the less interruption the better.

How Effective Is a Single Shock?

Most modern AEDs deliver a fixed-energy biphasic shock, commonly around 150 to 200 joules for adults. Data from AEDs used during actual out-of-hospital cardiac arrests show that a single shock at 150 joules successfully defibrillated about 96% of shockable rhythms, with the success rate climbing to nearly 99% after two shocks and over 99% after three.¹¹ This is why the AED cycles you through repeated rounds of CPR and re-analysis. If the first shock does not convert the rhythm, subsequent shocks often will.

Why You Should Not Stop to Check for a Pulse

The recommendation to immediately resume compressions after a shock can feel counterintuitive. You just delivered a potentially life-saving electrical jolt and the natural urge is to check whether it worked. But research analyzing post-shock rhythms found that even when the shock successfully terminates the abnormal rhythm, the heart often cannot produce a pulse right away. The myocardium is stunned, and without continued compressions to keep blood flowing, the person’s condition deteriorates.⁶ Guidelines emphasize that CPR should resume right after the shock without pausing to check pulse or rhythm.¹² The AED handles the timing. After two minutes, it will prompt you to stop compressions for another rhythm check.

Some AEDs now include real-time CPR feedback, using accelerometers to measure the depth and rate of your compressions and providing audio or visual cues to help you stay on target. These prompts can make a meaningful difference, particularly for people who have not practiced CPR recently.

Tricky Situations You Might Actually Face

A few scenarios cause people to freeze when they should be acting.

Wet surfaces: If the person is lying in a puddle or near a pool, drag them to a dry area if you can do so quickly. If not, wipe the chest dry and apply the pads. Testing of AEDs in wet environments, including pool water and salt water, found that the maximum voltage detected near the patient was well below hazardous levels, even at close range.¹³ The risk to bystanders from a shock delivered on a wet surface is minimal, but the pads need a dry chest to stick properly.
Medication patches: If you see a nitroglycerin or other medication patch on the chest where a pad needs to go, peel it off with a gloved hand (or use the pad packaging as a barrier) and wipe the area before placing the pad.
Implanted devices: If there is a visible lump under the skin of the upper chest (a pacemaker or implanted defibrillator), place the AED pad at least an inch away from it. Do not let this slow you down significantly.
Hairy chest: If the pads are not sticking because of chest hair, press them down firmly. If there is still no contact, rip the first set of pads off to remove hair, then apply a fresh pair.

None of these situations should stop you from using an AED. Delays caused by uncertainty about edge cases are far more dangerous than imperfect pad placement or a slightly damp surface.

Why So Many Bystanders Hesitate

Despite the fact that AEDs are designed for untrained users and do most of the decision-making themselves, bystander AED use rates remain low. Surveys consistently find that the two biggest barriers are lack of confidence in one’s skills and fear of legal consequences.¹⁴ A national survey in Taiwan found that concerns about technique and legal liability were the top barriers, and fewer than a third of respondents believed the public should use AEDs at the scene of a cardiac arrest.¹⁵

The legal reality in most of the United States and many other countries is that Good Samaritan laws protect bystanders who use an AED in good faith. In California, for example, an uncompensated person who uses an AED during an emergency is explicitly shielded from civil liability.¹⁴ Similar protections exist across most U.S. states and in many European and Asian countries, though the scope and specifics vary. The bottom line: the legal risk of using an AED is vanishingly small, while the risk of not using one when someone is in cardiac arrest is that the person dies.

What Happens After Paramedics Arrive

When EMS takes over, leave the AED pads attached. The device stores data, including the recorded heart rhythms, timestamps, and whether shocks were delivered. This information is valuable for the hospital team. Research has shown that in roughly one out of every eight or nine cardiac arrests, a shockable rhythm is captured only on the AED’s recording, not on any EMS or hospital monitor.¹⁶ That data helps doctors understand what happened and guides further treatment. Tell paramedics how many shocks were delivered, how long you performed CPR, and any other details you remember.

The Problem with AEDs That Are Not Ready When You Need Them

One underappreciated issue with public-access AEDs is maintenance. A five-year inspection study of public AEDs found that about 15% were not ready to use at the time of inspection. The most common reason was expired electrode pads, followed by device malfunctions and depleted batteries.¹⁷ Even more concerning, about 44% of inspected AEDs had some limitation on their 24-hour availability, often because the building they were kept in was locked outside business hours.

If you manage or oversee an AED at a workplace, gym, or community building, the maintenance obligation is straightforward: check the status indicator light regularly (most AEDs have a green light when ready), replace pads before their expiration date, and replace the battery on schedule. An AED that sits in a cabinet for years without attention may not work when someone’s life depends on it.

Where AEDs Make the Most Difference

Not all AED placements are created equal. Cost-effectiveness analyses show that AEDs provide the most value in locations where many people pass through and where cardiac arrests are more likely to occur and be witnessed: airports, large office buildings, transit stations, and similar high-traffic settings.¹⁸ AEDs in lower-traffic locations like small gyms or golf courses are less cost-effective from a strict public health perspective, though they still provide reassurance and raise awareness about sudden cardiac death. The visibility of a wall-mounted AED serves a secondary purpose: it normalizes the idea that anyone might need to use one and that doing so is expected, not heroic.