Sudden cardiac arrest (SCA) is one of the most serious medical emergencies a person can experience. It can happen without warning, and when it does, there’s only a brief window of time to act.
But in those critical minutes, the right response can dramatically improve the chance of survival.[1]
That’s when automated external defibrillators (AEDs) become life-saving tools.
AEDs provide step-by-step instructions so that any bystander, even without medical training, can take immediate action to save a life.
This guide will show you exactly how to use an AED. We'll walk through the essential steps, from preparation to activating the device.
You'll learn what to expect and how to respond with confidence when every second counts.
Originally published on January 10th, 2024, this article was updated and republished on May 26th, 2025.
What to Do Before Using an AED
Every emergency scene is different, and the environment may be chaotic. When someone has suddenly collapsed, bystanders may be unsure of what to do.
According to the American Heart Association, in any lifesaving situation, you should ensure the scene is safe. This means there should be no immediate danger, such as exposed electrical wires, fire, traffic, standing water, or unstable conditions, that could put you or others at risk.
If the person is lying in water, like a puddle, pool, or wet floor, move them to a dry area before using the AED. Moisture increases the risk of shock to both the victim and the responder.
If the area is unsafe and you can’t move the person safely, call for help and wait until professionals arrive.
Pro Tip: If you’re in a public space like a gym, airport, or community centre, AEDs are often stored in marked wall cabinets. When opened, the case may emit an audible alarm to alert others of an emergency, and that’s okay. Don’t hesitate to use it.
What Are the 7 Steps of Using an AED?
Below are the seven steps to follow when someone is experiencing SCA and you’re unsure how to use an AED. These steps will help you move quickly, calmly, and effectively through a high-stress situation.
Step 1: Ensure the Scene Is Safe
Before approaching the person, quickly assess your surroundings. Look for any potential dangers such as fire, traffic, live electrical wires, or unstable structures. Your safety comes first, so don’t put yourself or others at risk.
If the area is unsafe, call emergency services and wait for trained professionals. If the area appears safe, you can proceed to help the victim.
Step 2: Check for Responsiveness
Determine if the person is responsive. Approach them calmly and speak loudly, asking if they can hear you. Gently tap their shoulders to try and rouse them. If there’s no movement, no vocal reaction, and no signs of awareness, it’s time to act.
A person who is unresponsive, not breathing, and has no pulse is likely experiencing SCA. This means you need to act quickly.
Step 3: Call Emergency Services and Retrieve the AED
Once you’ve confirmed unresponsiveness, the next step is to call for help.
Dial 9-1-1 or your local emergency number immediately, or ask someone nearby to do it while you stay with the victim. If you’re in a public setting, direct someone to locate an AED. Many workplaces, schools, and recreational centres now keep one on-site.
The faster you retrieve and begin using the AED, the better the outcome may be.
Once the device is in hand, open it and power it on. Modern AEDs are designed to be intuitive and will begin issuing step-by-step instructions immediately upon activation, guiding you through what to do next.
Pro Tip: Use speakerphone if you're alone. This lets you communicate with dispatch while retrieving or using the AED.
Step 4: Check the Victim’s Breathing
After calling emergency services and retrieving the AED, check if the person is unresponsive and not breathing normally. Occasional gasping or irregular, shallow breaths do not count as effective breathing. These are signs of cardiac arrest.
If you're alone, grab the AED first, then return and start CPR. If someone is with you, ask them to retrieve the AED while you begin chest compressions.
If the person isn’t breathing normally, begin CPR right away. Every second without circulation reduces the chance of survival.
Most modern AEDs provide voice prompts to guide you through the process, including instructions for CPR. Follow these prompts closely and stay as calm as possible.
According to the American Heart Association, early CPR combined with AED use can double or even triple survival rates.
Step 5: Attach AED Electrode Pads
Attach the AED electrode pads to the victim's chest. Expose the chest and wipe it dry to ensure proper adhesion of the AED pads and accurate rhythm analysis.
One pad should be placed on the upper right side of the chest, just below the collarbone, and the other on the lower left side, beneath the armpit. This diagonal AED placement allows the electrical current to travel through the heart.
The pads are clearly marked and typically have visual diagrams to guide proper placement. Make sure they adhere firmly to bare skin, with no obstructions like clothing, jewelry, or moisture.
If the person has a visible implanted device, such as a pacemaker, place the pad at least one inch away from it. For children under eight years old or weighing less than 25 kg (55 lbs), use pediatric pads or switch the AED to pediatric mode if available.
Step 6: Analyze the Heart Rhythm
Once the defibrillator pads are in place, the AED will analyze the heart rhythm.
This process is fully automated, and the device will clearly alert you when it’s scanning. It’s critically important that no one touches the victim during this time. Physical contact can interfere with the AED’s ability to get an accurate reading.
The device is checking whether the heart is in a rhythm that can be corrected with a shock. After a few seconds, it will tell you what to do next: either deliver a shock or resume CPR.
Step 7: Administer the AED Shock (If Prompted)
If the AED determines that a shock is necessary, it will instruct you to deliver it. Semi-automatic models prompt you to press a button, while fully automatic models deliver the shock themselves after warning you to stand clear. Make sure no one is touching the victim during this step.
After the shock, the AED will either guide you to begin CPR or perform another analysis. Keep following the device’s prompts; many AEDs offer real-time coaching for CPR, rhythm checks, and shock instructions. Continue until help arrives or the person regains signs of life.
Performing CPR between shocks keeps blood flowing to vital organs and improves the chances of restoring a shockable rhythm.
Pro Tip: Most AEDs provide continuous voice prompts, including CPR coaching, rhythm analysis, and shock instructions. Keep listening and responding until emergency help arrives or the person shows signs of life.
FAQs
Where to Place AED Pads
The placement of AED pads is essential to ensure the electrical current flows properly through the heart.
Once the victim’s chest is exposed and dry, place the pads as directed by the diagrams included with the device.
One pad goes on the upper right portion of the chest, just below the collarbone. The second pad should be placed on the lower left side of the chest, beneath the armpit, and slightly toward the centre of the torso.
The pads must adhere well to clean, dry skin. Clothing should be removed completely, and any moisture or sweat should be wiped away.
What Action Should You Take While the AED Is Analyzing the Heart Rhythm?
When the AED announces that it’s analyzing the heart rhythm, your job is to ensure the victim remains completely untouched.
Even slight movement or contact from another person can interfere with the analysis and lead to an inaccurate reading, which is why this brief pause in compressions is so important.
Step back, ask others to do the same, and observe the victim without making contact. The AED will clearly state whether a shock is advised or if CPR should resume.
Trust the device to guide you. It’s programmed to detect shockable rhythms and make those decisions, so you can focus on staying calm and following the next instruction.
What Is the Most Appropriate First Step to Take as Soon as the AED Arrives at the Victim’s Side?
The first thing you should do when the AED arrives is to turn it on. Most models either have a clear power button or automatically activate when the lid is opened.
Starting the device immediately is crucial when learning how to use an AED. It ensures that voice prompts begin immediately, guiding you through each step without hesitation.
From that moment forward, the AED becomes your partner. It will give calm, direct instructions. It will tell you where to place the pads, when to stay clear, and whether a shock should be delivered.
Activating the AED immediately helps you move quickly and confidently. In a high-stress situation, having the device lead the way makes all the difference.
What Are Five Things You Should Not Do When Using an AED?
AEDs are designed to be simple and intuitive even in high-stress situations. Still, there are a few important things to watch out for to make sure the device works properly and everyone stays safe.
- Avoid Touching the Victim: Avoid touching the victim during the AED’s analysis or shock delivery. Physical contact at this stage can interfere with the device’s ability to assess the heart rhythm accurately and may pose a safety risk to anyone in contact.
- Skip the Alcohol: While it may seem helpful, alcohol can prevent the pads from sticking properly, and because it’s flammable, it introduces a serious hazard when electrical current is involved.
- Don’t Shock in Motion: Never attempt to use an AED in a moving vehicle. A stable surface is essential for accurate heart rhythm detection and safe shock delivery.
- Dry Before Defibrillating: Ifthe person is wet or lying in water, they should be moved to a dry area. Moisture on the chest must also be removed before pad placement to ensure proper adhesion and safe operation.
- Watch Your Footing: Avoid using the AED on conductive surfaces such as wet floors or metal bleachers. These surfaces can cause the shock to travel unpredictably, creating a risk to the victim and nearby responders.
Learn more in our AED FAQs.
Be Ready to Act. Every Second Matters.
Learning how to use an AED makes lifesaving action possible for anyone, not just medical professionals. When you understand how and when to use one, you’re not just gaining a skill.
You’re stepping into a role of courage, compassion, and leadership.
This knowledge isn’t just for rare situations. It’s a way to make your workplace, community, or home safer for everyone who enters it. And when you feel confident in your ability to respond, you’re no longer a bystander; you become an essential part of the chain of survival.
Looking for the right AED for your community? Check out our AED Buying Guide to compare different models.
If you have any questions, just reach out for personalized support. We’re here to help you find the best AED for your budget and needs.
References
[1] Weisfeldt, M. L., Sitlani, C. M., Ornato, J. P., Rea, T., Aufderheide, T. P., Davis, D., Dreyer, J., Hess, E. P., Jui, J., Maloney, J., Sopko, G., Powell, J., Nichol, G., Morrison, L. J., & the ROC Investigators. (2010). Survival after application of automatic external defibrillators before arrival of the emergency medical system: Evaluation in the Resuscitation Outcomes Consortium population of 21 million. Journal of the American College of Cardiology, 55(16), 1713–1720. https://pmc.ncbi.nlm.nih.gov/articles/PMC3008654/
