At a glance
- An AED analyses the heart’s rhythm during a cardiac arrest and delivers a shock when a shockable rhythm is detected.
- Built-in voice prompts guide even non-medical responders through the rescue process.
- CPR and defibrillation work together to support survival during cardiac arrest.
- Having an AED nearby can improve preparedness when cardiac emergencies happen away from public devices.
Cardiac arrest does not always come with a warning. It can happen at home, on a sports field or in the middle of an ordinary afternoon to someone with no known heart condition. Without rapid intervention, the chances of survival are low.
An automated external defibrillator, more commonly known as an AED, is one of the most important tools for responding to cardiac arrest during those first critical minutes. Yet many people have walked past one in a gym, airport or community venue without fully realising what it does, how it works or whether they could confidently use one in an emergency.
Understanding how an AED works is important because cardiac arrest is highly time-critical. The longer defibrillation is delayed, the lower the chance of survival becomes.
This article explains what an AED is, when it is used and how it saves lives during a cardiac arrest emergency.
What Is an Automated External Defibrillator?
An automated external defibrillator or AED is a device that analyses the heart’s rhythm and, if needed, delivers an electric shock to help restore a normal heartbeat. [1]
AEDs are used during sudden cardiac arrest, which is different from a heart attack, despite the two often being confused.
A heart attack occurs when blood flow to part of the heart is blocked. The heart usually continues beating and the person is often awake and experiencing symptoms such as chest pain or discomfort.
Sudden cardiac arrest is an electrical malfunction in the heart. The heart suddenly stops pumping blood effectively, causing the person to collapse, become unresponsive and stop breathing normally. It can happen without warning, even with people with no known heart condition.
Although AEDs are designed specifically for cardiac arrest situations, not every cardiac arrest can be treated with a shock. The device analyses the heart rhythm and will only deliver a shock if the rhythm is considered shockable.
AEDs are now commonly found in public spaces across Australia, including airports, gyms, shopping centres, schools and sporting facilities, helping improve access to emergency defibrillation in busy community environments.
However, public-access AEDs can only cover so much ground. Australians are now increasingly choosing to keep a portable AED at home, in the car, at a holiday house or while travelling because cardiac emergencies do not always happen near a fixed public device.
In Australia, every AED sold to the public must be listed on the Therapeutic Goods Administration’s (TGA) Australian Register of Therapeutic Goods (ARTG), helping ensure the device meets strict safety and performance standards.
How Does an AED Actually Work?
During sudden cardiac arrest, the heart can stop pumping blood effectively within seconds. Every minute that passes without intervention, the chances of survival drop by approximately 10%. [2]
To understand how an AED works, it helps to understand what happens during certain types of cardiac arrest. One of the most common dangerous heart rhythms is ventricular fibrillation, where the heart’s lower chambers quiver instead of pumping blood effectively.
This is considered a shockable rhythm, meaning an AED may be able to treat it with a controlled electrical shock.
Turn On the AED and Place the Pads As Directed
The first step is to turn the AED on. From that point, the device provides clear voice instructions to guide the responder through the process.
The responder places the electrode pads on the person’s bare chest in the positions shown on the device. Correct pad placement is important because it allows the AED to accurately analyse the heart’s electrical activity and deliver a shock effectively if one is required.
AED Determines Whether a Shock Is Needed
Once the pads are attached, the AED automatically analyses the heart’s rhythm to determine whether defibrillation is appropriate.
If a shockable rhythm such as ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) is detected, the device prepares to deliver a shock. If the rhythm is not shockable, the AED will not advise a shock. [1]
Unlike a person, the AED does not rely on judgment or guesswork. It uses built-in software to assess the heart’s electrical activity and determine whether a shock may help restore a more organised rhythm. This analysis happens within seconds and helps ensure a shock is only delivered when appropriate.
This built-in analysis is what allows AEDs to be safely used by members of the public, even without a medical background.
AED Delivers the Shock
If a shockable rhythm is detected, the AED charges and instructs everyone to stand clear to ensure no one is touching the patient. The device then delivers, or advises the delivery of, a controlled electrical shock through the chest, depending on the type of AED being used.
Some AEDs require the responder to press a shock button once the device has determined a shock is needed. Fully automatic AEDs, such as Elliot AED, deliver the shock automatically without requiring the responder to press a button. In both cases, the device analyses the heart rhythm and will only proceed if a shockable rhythm is detected.
The shock briefly interrupts the heart’s abnormal electrical activity, allowing it to resume a more organised rhythm.
Note: An AED does not restart a heart that has completely stopped. It is designed to correct certain dangerous rhythms where the heart is still experiencing chaotic electrical activity. [3]
What Happens After the Shock
After the shock is delivered, the AED prompts the responder to begin or resume CPR. CPR helps maintain blood flow to the brain and vital organs while the equipment continues monitoring the heart’s rhythm. [4]
The device periodically re-analyses the rhythm and advises another shock if needed. This cycle continues until emergency services arrive and take over care.
Why Having an AED Within Reach is Important
Understanding how an AED works is one thing. Having one available when a cardiac emergency happens is another.
Around 70% of sudden cardiac arrests occur outside hospitals, including at home, on the road or during everyday activities. While public AEDs in shopping centres, airports and sporting facilities improve access to emergency defibrillation, they are not always immediately available when and where a cardiac emergency occurs.
Because the chances of survival decrease with every minute defibrillation is delayed, proximity can make a meaningful difference during a cardiac arrest response.
This is one reason why ownership of portable defibrillators is becoming more common in Australia. Rather than relying solely on a publicly mounted device nearby, some individuals and families are choosing to keep an AED at home, in the car, at a holiday house or while travelling.
Devices such as the Elliot automated external defibrillator are designed with that type of accessibility in mind. Elliot is compact and lightweight, making it easier to keep a portable AED close at home, in the car or while travelling, rather than relying solely on fixed public-access devices.
The device is intended for non-medical users, with loud voice prompts and visual guidance to help responders act more confidently during high-stress situations, including in noisy environments. It is also listed on the TGA’s Australian Register of Therapeutic Goods (ARTG).
Broader conversations around defibrillator accessibility are also continuing at a legislative level. South Australia, for example, introduced requirements for AEDs in certain public and private sector facilities commencing January 2025. [5] While initiatives like this improve public access, cardiac arrests do not only happen in public places. In many situations, the only AED available is the one nearby.
An automated external defibrillator is not a complicated device. It analyses the heart’s rhythm, determines whether a shock is needed and guides the responder through the process. Much of the hesitation people feel around AEDs comes from unfamiliarity rather than the difficulty of using one.
Sudden cardiac arrest does not discriminate. It does not wait for a hospital nearby or a paramedic around the corner. It can happen in ordinary moments, to ordinary people, in ordinary places. In those moments, the difference between life and death can come down to what is within reach and whether the person nearby has the confidence to use it.
Understanding what an AED is and how it works is the first step. The next step is to consider whether one would be available if an emergency occurred close to home, on the road or in another everyday setting.
For those exploring personal AED ownership, the Elliot AED is designed to make defibrillation more accessible to non-medical users through its portable design, clear voice guidance and fully automatic operation.
FAQs
Can I accidentally shock someone who does not need a shock?
No. An AED will only advise or deliver a shock if it detects a shockable heart rhythm. If no shockable rhythm is present, the device will not deliver a shock. AEDs are specifically designed to guide non-medical users safely through the process with step-by-step voice prompts.
Can I get hurt using an AED?
AEDs are designed to be safe for responders to use. The device provides clear voice instructions and will advise everyone to stand clear while it analyses the heart rhythm or delivers a shock. As long as responders follow the prompts and avoid touching the person during analysis or shock delivery, the risk to bystanders is extremely low.
How many shocks can an AED deliver during a rescue?
There is no fixed number. The AED continuously analyses the person’s heart rhythm and will only advise a shock when a shockable rhythm is detected. After each CPR cycle, the device reassesses the heart and determines whether another shock is needed. This process continues until emergency services arrive or the heart rhythm changes.
Citation
- Heart Foundation – Automated External Defibrillators (AEDs) https://www.heartfoundation.org.au/heart-of-the-nation/aeds
- ScienceDirect – Decreasing the time of defibrillation (research paper) https://www.sciencedirect.com/science/article/abs/pii/S0196064404009400
- First Aid AE – Common defibrillator myths and AED functionality https://firstaidae.com.au/most-common-defibrillator-myths-debunked/
- Healthdirect – Defibrillators https://www.healthdirect.gov.au/defibrillators
- Heart Foundation – AED accessibility and public access initiatives https://www.heartfoundation.org.au/media-releases/shockingly-simple-to-save-a-life