Using an AED overview
Informed by recognized medical guidance
Overview
An AED (Automated External Defibrillator) is a portable device that checks a person's heart rhythm and can send an electric shock to the heart to try to restore a normal rhythm during sudden cardiac arrest. It is designed to be used by anyone, even without medical training.
Key facts
- An AED gives step-by-step voice instructions, so you don't need to be a doctor to use it.
- Using an AED within the first few minutes of cardiac arrest can greatly increase the person's chance of survival.
- AEDs are found in many public places like airports, gyms, shopping centres, and community centres.
AEDs are becoming more common in public spaces across the UK and many other countries. Sudden cardiac arrest happens to about 1 in 1,000 adults each year, and having an AED nearby can be life-saving.
AEDs are used when someone has a sudden cardiac arrest – when their heart stops beating effectively. This can happen to anyone, but it is more common in older adults and people with known heart conditions. However, it can also affect younger people, especially during exercise or due to certain heart conditions.
Symptoms
- Someone collapses and is not responding
- The person is not breathing normally
- You suspect a cardiac arrest
Common symptoms
- Sudden collapse and unconsciousness
- No normal breathing or only gasping
- No response when you tap and shout
Symptoms in children
- Sudden collapse, often during physical activity
- No normal breathing or gasping
- No response to stimulation
Symptoms in older adults
- Sudden collapse with no warning
- Possible chest pain or fainting just before collapse
- No normal breathing or only gasping
Causes
Main causes
- Heart attack (a blockage in the heart’s blood supply)
- Abnormal heart rhythms like ventricular fibrillation
- Severe lack of oxygen (e.g., drowning or choking)
- Electric shock or trauma to the chest
- Certain inherited heart conditions
Risk factors
- Coronary heart disease
- Previous heart attack
- Family history of sudden cardiac arrest
- Smoking, high blood pressure, diabetes, obesity
- Intense physical exertion in people with undiagnosed heart problems
When to see a doctor
See a doctor urgently if:
- If you or someone you know has fainted during exercise or has chest pain, seek same-day medical help
- If you have been resuscitated from a cardiac arrest, you will already be in hospital
Book a routine appointment if:
- If you have risk factors for heart disease, talk to your doctor about a heart health check
- If you have a family history of sudden cardiac arrest or inherited heart conditions
Diagnosis
An AED itself does not diagnose a condition – it analyzes the heart rhythm to decide if a shock is needed. After the person is in hospital, doctors diagnose the cause of the cardiac arrest using tests and examinations.
Tests that may be done
- Electrocardiogram (ECG) – to check heart’s electrical activity
- Blood tests – to check for heart damage or other problems
- Echocardiogram – an ultrasound of the heart
- Coronary angiography – to look at blood flow in the heart arteries
What to expect at your appointment
After a cardiac arrest, the person will be cared for in a hospital. Doctors will do tests to find out what caused the arrest and then plan treatment to prevent it happening again.
Treatment
When you see someone collapse and suspect cardiac arrest, start CPR (chest compressions) immediately and ask someone to find an AED. Turn on the AED and follow the voice prompts. It will tell you to place the pads on the person's bare chest and will analyze the rhythm. If a shock is advised, make sure no one is touching the person, then press the shock button. Continue CPR until emergency help arrives.
Self-care at home
- Learning CPR and how to use an AED can save a life. You can attend a local training course or find online resources.
- Keep emergency numbers and the location of nearby AEDs handy if you or a family member is at risk.
Medical treatments
After a cardiac arrest, hospital treatment may include medications to support the heart and prevent abnormal rhythms, procedures to open blocked heart arteries, or placement of a device like a pacemaker or implantable defibrillator. The exact treatment depends on what caused the arrest.
When is surgery considered?
In some cases, surgery such as coronary bypass grafting may be needed to improve blood flow to the heart. This will be decided by doctors based on test results.
Living with this condition
After surviving a cardiac arrest, your life may change in some ways. You will likely need regular follow-up with a heart specialist (cardiologist). You may be prescribed medications and advised on lifestyle changes.
Lifestyle tips
- Avoid smoking and limit alcohol
- Manage stress with relaxation or mindfulness
- Follow your doctor’s advice about physical activity and driving restrictions
- Learn to recognise early warning signs of heart problems, such as chest pain or fainting
Diet and exercise
A heart-healthy diet rich in fruits, vegetables, whole grains, and lean proteins is recommended. Your doctor will advise on safe exercise – often a gradual return under supervision.
Mental health and emotional wellbeing
Surviving a cardiac arrest can be emotionally tough. You may feel anxious, depressed, or fearful of it happening again. It is important to talk about these feelings with your doctor or a counsellor.
Prevention
While not all cardiac arrests can be prevented, you can reduce your risk by adopting a heart-healthy lifestyle, managing health conditions like high blood pressure and diabetes, and following your doctor’s advice. Knowing how to use an AED and learning CPR helps improve survival if someone does arrest.
Screening programmes
If you have a strong family history of heart disease or sudden cardiac arrest, your doctor may recommend heart screening tests like an ECG or echocardiogram. This is done on a case-by-case basis.
Complications
If left untreated
- Without immediate CPR and AED use, a person in cardiac arrest will die within minutes
- Even with treatment, some people may have brain damage due to lack of oxygen
- Other organs may be affected if blood flow is not restored quickly
Long-term outlook
The outlook depends on how fast the person receives help. For every minute without CPR and defibrillation, the chance of survival drops by about 10%. With prompt action, many people survive to hospital and go on to live full lives. Ongoing medical care and lifestyle changes greatly improve long-term chances.
Find support
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 21, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.