FAQ

The Circuit is the national defibrillator network for the UK, operated by the British Heart Foundation on behalf of NHS England. It is a register of publicly accessible AEDs \u2014 defibrillators that can be used by any bystander in an emergency.

When you call 999 about a cardiac arrest, ambulance dispatchers can access The Circuit to identify and direct bystanders to the nearest registered AED, potentially saving vital minutes.

You can also search for AED locations yourself at thecircuit.org.uk or via the NHS app.

If you have a defibrillator \u2014 in a sports club, workplace, school, church, or community building \u2014 registering it on The Circuit means it will show up to 999 dispatchers in an emergency. Registration is free and takes only a few minutes. It could mean the difference between life and death for someone in your community.

Using an AED is straightforward. The device is designed for bystanders with no medical training and gives clear spoken and visual instructions at every step.

1. Switch the AED on. Most devices power on when you open the lid or press a button.

2. Follow the spoken instructions. The AED will tell you exactly what to do.

3. Attach the pads. Remove or cut through clothing to expose the bare chest. Peel the pads from their backing and attach them in the positions shown in the pictures on the pads themselves \u2014 one below the right collarbone, one on the left side below the armpit.

4. Let the AED analyse the heart rhythm. Stay still and make sure no one is touching the person while the AED analyses. It will tell you not to touch.

5. Deliver a shock if advised. If a shock is needed, the AED will charge and tell you to press the shock button (or, on fully automatic devices, will deliver the shock itself). Make sure no one is touching the person before pressing the button.

6. Resume CPR immediately. As soon as the shock is delivered, restart chest compressions. The AED will prompt you to continue CPR and will analyse the rhythm again after two minutes.

If the AED advises no shock is needed, continue CPR. The AED will reassess regularly and advise if a shock becomes appropriate.

You cannot accidentally shock someone who does not need it \u2014 the AED will only allow a shock if the rhythm requires it.

If you find someone who has collapsed and is unresponsive, follow these steps:

1. Check for danger. Make sure it is safe to approach.

2. Check for a response. Tap their shoulders and shout "Are you alright?"

3. Call for help. Shout for someone nearby to help you.

4. Open the airway. Tilt the head back gently and lift the chin.

5. Check for normal breathing. Look, listen, and feel for no more than 10 seconds. Occasional gasps are not normal breathing.

6. Call 999 immediately \u2014 or ask someone else to call while you start CPR. Tell the dispatcher the person is not breathing. They will guide you through CPR.

7. Send someone for the nearest AED. Ask a bystander to find one \u2014 the 999 dispatcher can give the location of the nearest registered device.

8. Start CPR. Place both hands on the centre of the chest and push down hard and fast \u2014 5\u20136cm deep at 100\u2013120 compressions per minute. Do not stop until the ambulance arrives or an AED is ready.

9. Use the AED as soon as it arrives. Switch it on and follow the spoken instructions.

If there are other people with you, one person should do CPR while another calls 999 and a third goes for the AED. Do not leave the person alone if you can help it.

It is unlikely. Studies show that AEDs interpret the victim’s heart rhythm more quickly and accurately than many trained emergency professionals. If the AED determines that no shock is needed, it will not allow a shock to be given.

AEDs are safe to use by anyone who has been shown how to use them.

The AED’s voice guides the rescuer through the steps involved in saving someone; for example, “apply pads to patient’s bare chest” (the pads themselves have pictures of where they should be placed) and “press red shock button.” Furthermore, safeguards have been designed into the unit precisely so that non-medical responders can’t use the AED to shock someone who doesn’t need a shock.

Use an AED on anyone who is unresponsive and not breathing normally. If in doubt, use it. The AED will analyse the heart rhythm and will not allow a shock to be delivered unless one is actually needed. You cannot make the situation worse by using it.

It doesn’t matter. Treating cardiac arrest is a high-stress situation, and even experienced healthcare providers do not do everything perfectly. Performing CPR and using an AED — however imperfectly — can only help. Imperfect action is always better than inaction.

No. If you used an AED promptly and correctly, you did everything right. Unfortunately, not every person in cardiac arrest can be saved, even with fast and accurate treatment. Some underlying medical or cardiac conditions mean that ventricular fibrillation cannot always be corrected by defibrillation, regardless of how quickly it is delivered.

Acting quickly and using the AED gave that person the best possible chance. That matters, even when the outcome is not what you hoped for. If you are struggling with the experience, please talk to your GP or contact SCA UK for peer support.

The chest should be exposed to allow the placement of the disposable electrode pads. A woman’s bra should be removed. Clothes may need to be cut off.

AEDs are extremely safe when used properly. The electric shock is designed to go from one electrode pad to another through the victim’s chest. Basic precautions, such as verbally warning others to stand clear and visually checking the area before and during the shock, can maximise the safety of rescuers.

CPR provides some circulation of oxygen-rich blood to the victim’s heart and brain. This circulation delays both brain death and the death of heart muscle. CPR also makes the heart more likely to respond to defibrillation.

Start CPR immediately. Once the AED is present, apply the electrode pads to the victim’s bare chest, and follow the AED’s voice prompts and messages. It will tell you when to resume CPR.

There is no specific legal requirement for employers to provide defibrillators in the workplace. The Health and Safety Executive’s syllabus of first aid training for offshore installations does include the use of defibrillators, but this is not extended to onshore first aid. However, the Health and Safety (First-Aid) Regulations 1981 do not prevent an employer from providing defibrillators that could benefit both their employees and the public.

For information on workplace health and safety legislation please refer to the Health and Safety Executive’s website.

If you think an AED should be installed in your workplace, read the Guide to AEDs written by Resuscitation Council UK and the BHF as this will answer your questions in detail. If you wish to proceed, contact your local ambulance service for further advice as described in the Guide.

Yes. Whilst SCA in school-age children is rare, resuscitation attempts at schools are more likely to be made on an adult — a staff member or visitor — than a pupil. An AED on site provides potential benefit for everyone present, not just students.

Having a prominently located AED also means students become familiar with the equipment and can learn about resuscitation and defibrillation as part of first aid education — a benefit that extends well beyond the school gates.

Since September 2023, all state-funded schools in England have been required by law to have at least one AED on site. The Resuscitation Council UK guidance on defibrillators in schools provides detailed advice on placement, maintenance, and training. The Department for Education has also published guidance on AEDs in schools covering legal requirements and best practice.

Yes. Fortunately, cardiac arrest is rare in people who are pregnant, but if it were to occur it is quite appropriate to use an AED. The procedure is the same as in the non-pregnant but it is important to place the pads clear of enlarged breasts.

Yes. The incidence of shockable rhythms requiring defibrillation in children is very low but can occur. The priority must always be for high-quality CPR and getting expert help. However, the AED can be used across all age groups if this is the only available machine.

The paediatric advanced life support Guidelines 2015 state that if using an AED on a child of less than eight years, a paediatric attenuated shock energy should be used if possible. 

Experience with the use of AEDs (preferably with dose attenuator) in children younger than one year is limited. The use of an AED is acceptable if no other option is available as, on balance, it is probably better to give a 50 J shock than nothing at all. The upper safe limit for dosage in this group is unknown.

AEDs have been used by untrained people to save lives. Clear, spoken instructions and visual illustrations guide users through the process. Lack of training should not be a barrier to someone using one. If a person is in cardiac arrest, do not be afraid to use an AED.

Public Access Defibrillation describes the use of AEDs by members of the public. AEDs can now be found in many busy public places including airports, mainline railway stations, shopping centres, and gyms. They are meant to be used by members of the public if they witness a cardiac arrest.

AEDs are very reliable and will not allow a shock to be given unless it is needed. They are extremely unlikely to do any harm to a person who has collapsed in suspected Sudden Cardiac Arrest. They are safe to use and present minimal risk to the rescuer. These features make them suitable for use by members of the public with little or no training).

Resuscitation Council UK and British Heart Foundation have written a Guide to Automated External Defibrillators (AEDs) which gives full information about the use of AEDs in the community. We urge you to read this as it will answer your questions in more detail.

Yes, it is safe to defibrillate a victim who is lying on a metallic or wet surface. If the self-adhesive pads are applied correctly and provided there is no direct contact between the user and the victim when the shock is delivered, there is no direct pathway that electricity could take that would cause the user to experience shock. 

If the victim is wet, their chest should be dried so that the self-adhesive AED pads will stick properly. As with any attempt at defibrillation, particular care should be taken to ensure that no one is touching the victim when a shock is delivered.

No. In the UK, it is very unlikely that someone who acted in good faith when trying to help a person in cardiac arrest would face any legal liability. No action has ever been successfully brought against a bystander who performed CPR in the UK. The courts look favourably on those who go to the assistance of others in an emergency, and performing CPR on someone in cardiac arrest cannot make their situation worse. If you are concerned, the important thing is simply to act — calling 999, starting CPR, and using a defibrillator if one is available. For specific legal questions, the Resuscitation Council UK provides further guidance.

People who are at risk for SCA may want to consider having an AED at home. Regardless of known risk, since seven out of 10 SCAs occur at home, placing these devices in homes could save many lives.

No. CPR and an AED work together and neither replaces the other. They do different jobs at different stages of the resuscitation process.

CPR keeps oxygenated blood circulating to the brain and heart while the heart is not beating. It does not restart the heart, but it delays the onset of irreversible brain damage and keeps the heart muscle responsive to defibrillation. Without CPR, the window in which an AED can work effectively narrows quickly.

An AED delivers an electrical shock to reset the heart’s rhythm when it is in ventricular fibrillation or pulseless ventricular tachycardia. This is what CPR alone cannot do. The shock is what restores a normal heartbeat.

The correct sequence is: call 999, start CPR immediately, apply the AED as soon as it arrives, follow the AED’s instructions, and resume CPR straight after each shock analysis. Do not stop CPR while waiting for an AED, and do not stop using the AED once it arrives.

The defibrillators used by paramedics on ambulances, in hospital settings, and the ones you typically see on TV are manual defibrillators. They are larger than AEDs, require interpretation of the heart rhythm by a trained operator, and must be charged and discharged manually.

AEDs are smaller, computerised devices designed for use by any bystander. They analyse the heart rhythm automatically, decide whether a shock is needed, and guide the user through every step with audio and visual prompts. They will not deliver a shock unless one is required.

Good locations for AED placement include police vehicles, airports, railway and bus stations, sports venues, GP surgeries and dental practices, health clinics, gyms, shopping centres, supermarkets, theatres, workplaces, schools, places of worship, and community centres. In the UK, AED locations can be found using The Circuit — the national defibrillator network (thecircuit.org.uk) — and through many local ambulance service mapping tools. The British Heart Foundation and St John Ambulance also provide guidance on siting and registering AEDs. Since the majority of out-of-hospital cardiac arrests occur in the home, some people at high risk may also consider purchasing an AED for home use.

AEDs are designed to treat victims in SCA with an irregular heart rhythm called ventricular fibrillation (VF). AEDs work best in these victims if they are used quickly and if the victim has received cardiopulmonary resuscitation (CPR).

If the victim has an implantable pacemaker or defibrillator with a battery pack (visible as a lump under the skin), avoid placing the pad directly on top of the implanted medical device.

Never place AED electrode pads directly on top of medication patches. If the patch is in the way of the AED pads, remove it and wipe off the area with the victim’s shirt. Do not touch the patch with bare skin. Then apply the pads to the clean, bare skin.

If the victim is wearing a bra, remove it before placing electrode pads.

Yes. An AED can be used safely on someone lying on a metal surface such as stadium seating, a metal bench, or a stretcher. The key requirement is that the self-adhesive electrode pads must not be in direct contact with the metal surface itself. As long as the pads are correctly placed on the person’s bare chest, there is no pathway for electricity to pass to the metal beneath them.

No, not if you use it properly. The electric shock is programmed to go from one pad to the other through the victim’s chest. Basic precautions, such as not touching the victim during the shock, ensure the safety of rescuers and bystanders.

No. Most SCA victims will die if they are not treated immediately. Your actions can only help. AEDs are designed in such a way that they will only shock victims who need to be shocked.

An AED is designed for use by any bystander, regardless of training. The AED uses voice and visual prompts to advise the user how to apply electrode pads and whether or not to administer a shock. Some devices shock automatically if the victim has a fatal heart rhythm. Training is recommended since many victims also need CPR (cardiopulmonary resuscitation).

A computer inside the AED analyzes the victim’s heart rhythm. The device determines whether a shock is needed. Some devices shock the victim automatically if a shock is needed. Other devices require that the operator press a button to deliver the shock. The shock is delivered through pads applied to the victim’s bare chest. The shock stuns the heart, stopping abnormal heart activity and allowing a normal heart rhythm to resume.

An AED, or automated external defibrillator, is a device that automatically analyzes heart rhythms and advises the operator to deliver a shock if the heart is in a fatal heart rhythm. It is designed for use by untrained bystanders. AEDs are safe and cannot hurt the victim.

SCA is treatable in most cases — especially when it is caused by ventricular fibrillation — as long as treatment is given quickly. Treatment requires cardiopulmonary resuscitation (CPR) and defibrillation. This must begin immediately to be effective, ideally within three to five minutes of collapse. Even the fastest ambulance response may not arrive in time. That is why prompt action by bystanders is critical, and why learning CPR and how to use an AED can save lives.

If someone is unresponsive and not breathing normally, suspect cardiac arrest and act immediately: call 999, start CPR, and use a nearby AED if one is available. The dispatcher will guide you through CPR if you are unsure. When cardiac arrest occurs, the person is clinically dead, but prompt bystander action can restore life.

Once the ambulance service arrives, paramedics will continue resuscitation and provide advanced cardiac life support. Patients who remain in a coma after successful resuscitation may be treated with targeted temperature management (controlled cooling) to protect the brain. All survivors of cardiac arrest should be reviewed by a cardiologist or cardiac electrophysiologist for follow-up assessment and treatment.

The easiest way to find your nearest publicly accessible defibrillator is through The Circuit — the national defibrillator network operated by the British Heart Foundation on behalf of the NHS. The Circuit maps registered AEDs across the UK and is accessible online or via the NHS app.

When you call 999 about a cardiac arrest, the dispatcher can also tell you the location of the nearest registered defibrillator and guide someone to collect it while CPR is in progress.

You can also visit our defibrillator maps page, which lists additional national and local mapping resources.