Quick answer
An automated external defibrillator (AED) is a portable device that can restart a heart in sudden cardiac arrest. Call Triple Zero (000) and start CPR, then as soon as an AED arrives: turn it on, attach the pads to the bare chest, stand clear while it analyses the heart rhythm, press the shock button if it tells you to, and continue CPR. Modern AEDs talk you through every step and will only deliver a shock if one is needed.
If someone collapses in sudden cardiac arrest, the two things that save their life are early CPR and early defibrillation. An automated external defibrillator (AED) is designed so that anyone can use it — you do not need to be trained, and you cannot accidentally shock someone who does not need it. This guide explains what a defibrillator is, when to use one, exactly how to use an AED step by step, where the pads go, and how it fits into the DRSABCD action plan.
What is a defibrillator (AED)?
A defibrillator is a device that delivers a controlled electric shock to the heart. The type found in public places, workplaces and homes is an automated external defibrillator (AED) — a small, portable unit with two adhesive electrode pads and clear voice prompts. In sudden cardiac arrest the heart often falls into a chaotic, quivering rhythm called ventricular fibrillation; it cannot pump blood, and the person collapses and stops breathing normally. An AED analyses that rhythm and, if a shock can help, delivers one to give the heart the chance to restart a normal beat. The Australian Resuscitation Council (ANZCOR) and St John Ambulance Australia both recommend using an AED as early as possible alongside CPR.
Why speed matters: survival from cardiac arrest falls by roughly 10% with every minute that passes without CPR and defibrillation. Using a public access defibrillator early, before paramedics arrive, can more than double someone's chance of survival.
When to use a defibrillator
Use an AED when a person is unconscious and not breathing normally — the signs of cardiac arrest. Send someone to call Triple Zero (000) and to find the nearest defibrillator while you start CPR. The table below sets out when an AED is used and when it is not.
| Situation | What to do |
|---|---|
| Unconscious, not breathing normally | Call 000, start CPR, and use an AED as soon as one arrives. |
| Unconscious but breathing normally | Do not use an AED. Place in the recovery position and monitor breathing. |
| Conscious | An AED is not needed. Reassure, monitor, and treat any injuries. |
| Water or a metal surface | Move the person to a dry surface and dry the chest before attaching pads. |
How to use an AED: the step-by-step sequence
Work through these defibrillator steps calmly. The AED gives you a voice prompt for each one, and the Triple Zero operator can guide you too. Keep doing CPR while the AED is being fetched and switched on.
Before the AED arrives: confirm the person is unconscious and not breathing normally, make sure 000 has been called, and start CPR — 30 chest compressions to 2 breaths.
| Step | What you do |
|---|---|
| 1 | Turn the AED on and follow the voice prompts. This is the only thing you must remember — the device guides the rest. |
| 2 | Expose and dry the chest. Remove or cut through clothing; wipe away sweat or water so the pads stick. |
| 3 | Attach the pads to the bare chest, following the picture on each pad (see pad placement below). |
| 4 | Stand clear while the AED analyses the heart rhythm. Make sure no one is touching the person. |
| 5 | If a shock is advised, check everyone is clear and press the flashing shock button. (Fully automatic AEDs deliver it themselves.) |
| 6 | Resume CPR straight away, starting with chest compressions, and keep following the prompts. |
| 7 | Leave the pads on and keep going until the person recovers, paramedics take over, or you are told to stop. |
Where to place the AED pads (pad placement)
Correct AED pad placement matters because the shock needs to pass through the heart. Each pad has a picture showing where it goes, so you do not have to remember — but the standard adult placement is: one pad on the upper right chest, just below the collarbone, and the other on the left side, a little below the armpit. Press each pad down firmly onto bare, dry skin so there are no air gaps.
A few practical points on pad placement: if the chest is very hairy and the pads will not stick, shave or wipe the area quickly. Do not place a pad directly over a visible pacemaker lump or a medication patch — move it a few centimetres to the side. For a child under about eight or under 25 kg, use paediatric pads if the AED has them; if not, adult pads are still better than no defibrillation — place one pad on the centre of the chest and one on the back.
How a defibrillator works and what it does
When you attach the pads, the AED reads the heart's electrical rhythm through them. It is looking for a shockable rhythm — most often ventricular fibrillation, where the heart quivers instead of pumping. If it finds one, it charges and tells you a shock is advised. The shock briefly stops all electrical activity in the heart, giving the heart's natural pacemaker the chance to restart a coordinated, normal beat. If the rhythm is not shockable, the AED will say no shock is advised and prompt you to continue CPR — chest compressions keep blood moving to the brain and heart until a shockable rhythm returns or help arrives.
An AED will not shock a heart that does not need it. The device only delivers a shock when it detects a shockable rhythm — so you cannot harm someone by attaching one to a person who turns out not to need it.
Can you use a defibrillator wrong, or hurt someone with it?
This is the most common worry, and it is the reason some people hesitate — so it is worth answering plainly. You cannot hurt someone by attaching an AED. Modern defibrillators analyse the heart rhythm first and will only allow a shock if one is needed; if the rhythm is normal or absent, the device simply will not shock. The voice prompts walk you through every step in order, so there is no sequence to memorise. The only real mistake is not using one at all: in sudden cardiac arrest, doing nothing is the outcome to avoid. The single safety rule to follow is to make sure no one is touching the person at the moment a shock is delivered.
Where the defibrillator fits in DRSABCD
The defibrillator is the D (Defibrillation) — the final step of the DRSABCD action plan, the basic life support sequence used across Australia. After you have checked for Danger, Response, Sent for help, opened the Airway, checked Breathing and started CPR (Compressions), attaching an AED as soon as one arrives is what completes the chain. The earlier in the sequence the defibrillator is used, the better the chance of survival.
While you wait with the casualty or hand over to paramedics, check their wrist and neck for a medical ID. A medical ID can tell a responder what they cannot ask an unconscious patient — conditions, medications and who to contact — and it may carry a membership number for an online medical records service such as MedibandPlus.
With MedibandPlus, that membership number lets first responders access a secure profile that stores the wearer's health conditions, medications and next-of-kin contact. It does not assess or diagnose anything — it simply makes the wearer's own information available when they cannot speak, so the right care reaches them sooner and their family is contacted quickly.
Part of the Mediband family. Designed in Australia since 2004.
Related first aid guides: the full DRSABCD action plan, the recovery position, the COWS response check, and anaphylaxis first aid. When you are ready, you can start a MedibandPlus membership.
Defibrillator (AED) FAQs
How do you use a defibrillator?
Turn the AED on and follow its voice prompts: attach the pads to the bare, dry chest, stand clear while it analyses the heart rhythm, press the shock button if it advises one, then resume CPR. Keep going until the person recovers or paramedics take over.
When should you use a defibrillator?
Use an AED when a person is unconscious and not breathing normally — the signs of cardiac arrest. Call Triple Zero (000), start CPR, and use the AED as soon as one is available.
Where do you place the defibrillator pads?
For an adult, place one pad on the upper right chest just below the collarbone, and the other on the left side a little below the armpit. Each pad has a picture showing where it goes. Avoid placing a pad over a pacemaker or medication patch.
Can you hurt someone with a defibrillator?
No. A modern AED analyses the heart rhythm and only allows a shock if one is needed, so you cannot shock someone who does not need it. The only safety rule is to make sure no one is touching the person when a shock is delivered.
What does a defibrillator do?
It delivers a controlled electric shock that briefly stops a chaotic heart rhythm, giving the heart the chance to restart a normal beat. If the rhythm is not shockable, it prompts you to continue CPR instead.
Sources
- ANZCOR Guideline 7 — Automated external defibrillation in basic life support — when to attach an AED, pad placement, and how defibrillation fits alongside chest compressions.
- St John Ambulance Australia — defibrillation and first aid training.
- healthdirect — CPR — how CPR works and why compressions continue between shocks.
- Triple Zero (000) — when and how to call Australia’s emergency number, and what the call taker will ask you.
Disclaimer: This article is general first aid information, not medical advice or a substitute for accredited first aid training. In an emergency, always call Triple Zero (000). MedibandPlus stores and provides access to a member's own medical information; it does not monitor, assess or diagnose any condition.
