When someone suddenly collapses, every second matters. Confusion can set in during those first few moments, but knowing when to use an AED and how to act can save a life.
This guide breaks down the basics so you can recognize the signs, respond confidently, and understand what to do in real-world emergencies.
Originally published on January 10th, 2024, this article was updated and republished on May 12th, 2025.
The Basics of When to Use an AED (3 Things You Need to Know)
An Automated External Defibrillator (AED) is a portable device that can restart a person’s heart when it suddenly stops beating effectively.
Here’s what to check before using an AED:
- They are unresponsive (unconscious)
- They are not breathing normally
- They have no pulse or signs of circulation
These three signs point to sudden cardiac arrest, a condition in which the heart stops pumping blood effectively. It can happen without warning, even in seemingly healthy people. So, when you spot these signs, use an AED as soon as possible.
AEDs are often located in public places like gyms, airports, community centres, schools, and workplaces. If you don’t see one immediately, look for signs or ask nearby staff. Many are stored in visible, wall-mounted cases.
When Should an AED Not Be Used
While AEDs are powerful, they’re also smart. They won’t deliver a shock unless it’s needed, even if you press the button. That’s why trying is always better than hesitating.
That being said, here are a few cases where an AED is not necessary:
The Person Is Conscious and Breathing Normally
If they’re awake, alert, or even just breathing steadily, there’s no need for an AED. Instead, stay with them, keep them calm, and monitor their condition until help arrives.
The Person Has a Steady Pulse
Even if they seem ill or confused, if they have a pulse and are breathing, don’t use the AED. It’s designed to act only when the heart’s rhythm is dangerously off or has stopped altogether.
The Area Is Unsafe
If there’s standing water, fire, live electricity, or structural hazards nearby, don’t put yourself at risk to use the AED. Move the person to safety if possible, or wait for emergency services.
Emergency Response Steps When Using an AED
When someone suddenly collapses, it’s important to act fast, but first, you need to assess the situation. These steps will help you determine whether an AED is needed and guide you through what to do next.
1. Recognize the Emergency
Approach the person and try to wake them by tapping their shoulders and speaking loudly. If they don’t respond, check to see if they’re breathing normally. Occasional gasps or shallow, irregular breaths do not count as normal breathing.
Then check for a pulse. If the person is unresponsive, not breathing normally, and shows no signs of circulation, it’s time to act.
2. Call 911
Once you've identified the person in distress, call emergency services immediately. If someone else is nearby, ask them to make the call so you can continue assisting.
Be clear with the dispatcher: explain that the person is unresponsive, not breathing normally, and may be in cardiac arrest. Keep the phone on speaker if possible so you can follow any instructions while continuing to help.
3. Start CPR
Immediately begin chest compressions.
Kneel beside the person, place one hand in the centre of their chest, place your other hand on top, and begin pushing down hard and fast.
Aim for a consistent rhythm—about two compressions per second or 120 per minute. If you’ve been trained in CPR, include rescue breaths by giving two breaths after every 30 compressions.
If you haven’t had training, stick with continuous compressions. The goal is to keep blood and oxygen flowing to the brain and other vital organs until defibrillation is possible.
4. Get the AED
Ask someone to retrieve the nearest AED while you continue CPR. If you’re alone and an AED is within quick reach, get it after calling 911. Then, return to the person and resume care immediately.
5. Use the AED
As soon as the AED arrives, power it on. The device will begin speaking and provide clear, step-by-step instructions to guide you through the process.
Open the person’s shirt to expose their chest and apply the electrode pads as illustrated on the device. One pad typically goes on the upper right side of the chest and the other on the lower left side.
The AED will then analyze the person’s heart rhythm and advise whether a shock is needed. If a shock is recommended, ensure no one touches the person and press the shock button when prompted.
After the shock, resume CPR immediately unless the person shows clear signs of recovery, like normal breathing or movement. The AED will continue to guide you, and you should follow its instructions until emergency responders arrive and take over.
Common AED Emergency Scenarios
Sudden cardiac arrest doesn’t always look the same. These real-world examples can help you recognize when to use an AED quickly and confidently.
Sudden Collapse
If someone suddenly collapses without warning and doesn’t respond to your voice or touch, it may be a sign of sudden cardiac arrest. Check their breathing and pulse, and if either is absent or abnormal, begin CPR and use an AED immediately.
Drowning or Near-Drowning
When someone is pulled from water and is unresponsive or not breathing normally, cardiac arrest is a serious risk, even if the initial cause was a lack of oxygen rather than a heart issue.
Start CPR right away and use an AED to determine if a shockable rhythm is present.
Electrocution
The heart can go into an abnormal rhythm or stop entirely after an electric shock, whether from a household current, a downed power line, or a lightning strike. If the person collapses or becomes unresponsive, use an AED immediately.
Collapse During Exercise
If a person collapses while running, training, or playing sports, especially if they’re young and previously healthy or an older adult with risk factors, it’s safest to assume cardiac arrest. Don’t wait for confirmation; begin CPR and apply an AED as soon as it’s available.
Performing CPR and Using an AED: What You Need to Know
If both CPR and an AED are available, understanding when to use an AED alongside chest compressions gives the person the best chance of survival.
Start CPR Immediately
If someone is in cardiac arrest and an AED isn’t available yet, start CPR immediately. While CPR can’t restart the heart, it can buy precious time until a defibrillator arrives.
Use the AED As Soon As It Arrives
Once you have the AED, stop compressions briefly to apply the pads. Remember, you don’t need to be trained to use an AED; they’re designed for anyone to use safely and effectively.
Keep Going Until Help Arrives
Even after the AED delivers a shock, keep doing CPR unless the person starts breathing normally. The heart may need time to recover, and chest compressions help maintain blood flow during those critical moments.
Don’t stop unless the person wakes up or emergency responders take over. Consistent CPR can make the difference between life and death.
Don’t Be Afraid to Act
Sudden cardiac arrest can happen anywhere, to anyone, and in those first few minutes, you are the first responder. Recognizing the signs, starting CPR, and using an AED right away can dramatically increase someone’s survival rate.[1]
Not sure which AED is right for you? Don’t worry, we’re here to help. Contact us and we’ll walk you through the entire process so you get the absolute best AED for your 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/
