How to use a Defibrillator

Defibrillators are very easy to use. Although they don’t all look the same, they all function in broadly the same way. You don’t need training to use one. The machine gives clear spoken instructions – all you have to do is follow them – and it won’t shock someone unless they need it.

If you come across someone who is unconscious, unresponsive, not breathing or not breathing normally, they’re in cardiac arrest. The most important thing is to call 999 and start CPR to keep the blood flowing to the brain and around the body. After a cardiac arrest, every minute without CPR and defibrillation reduces someone’s chance of survival by 10 percent. If you’re on your own, DON’T interrupt the CPR to go and get a defibrillator. If it’s possible, send someone else to find one. When you call 999, the operator can tell you if there’s a public access defibrillator nearby. To use a defibrillator, follow these simple steps:

  • Step 1: Turn the defibrillator on by pressing the green button and follow its instructions.
  • Step 2: Peel off the sticky pads and attach them to the patient’s skin, one on each side of the chest, as shown in the picture on the defibrillator.
  • Step 3: Once the pads have been attached, stop CPR and don’t touch the patient. The defibrillator will then analyse the patient’s heart rhythm.
  • Step 4: The defibrillator will assess whether a shock is needed and if so, it will tell you to press the shock button. An automatic defibrillator will shock the patient without prompt. Do not touch the patient while they are being shocked.
  • Step 5: The defibrillator will tell you when the shock has been delivered and whether you need to continue CPR.
  • Step 6: Continue with chest compressions and rescue breaths until the patient shows signs of life or the defibrillator tells you to stop so it can analyse the heartbeat again.

 Cardiac Arrest

A cardiac arrest is when your heart suddenly stops pumping blood around your body. When your heart stops pumping blood, your brain is starved of oxygen. This causes you to fall unconscious and stop breathing.

What Are the Signs of a Cardiac Arrest?

A cardiac arrest usually happens without warning. If someone is in cardiac arrest, they collapse suddenly and:

  • will be unconscious
  • will be unresponsive
  • won’t be breathing or breathing normally – not breathing normally may mean they’re making gasping noises.

Without immediate treatment or medical attention, the person will die. If you see someone having a cardiac arrest, phone 999 immediately and start CPR.

CPR in 5 steps

Step 1: Shake and shoaut

If you come across someone who is unconscious, always check for danger and look for risks before you start helping.

Someone having a cardiac arrest will either not be breathing or they won’t be breathing normally. They also won’t be conscious.

Check for a response – gently shake the person’s shoulders and ask loudly ‘are you alright?’

Shout for help – if someone is nearby, ask them to stay as you might need them. If you are alone, shout loudly to attract attention, but don’t leave the person.

Step 2: Call 999

If the person is not breathing or not breathing normally:

  • Ask someone to call 999 immediately and ask for an ambulance
  • Ask someone for a public access defibrillator (PAD).
  • If there’s no one around call 999 before starting compressions.

Step 3: Cover mouth and nose with cloth.

  • If you think there’s a risk of infection, lay a towel or a piece of clothing over the mouth and nose. Don’t put your face close to theirs. 
  • If you’re sure the person is breathing normally, put them in the recovery position.

Step 4: Give chest compressions

Do not give rescue breaths at this time.

  • Kneel next to the person.
  • Place the heel of one hand in the centre of their chest. Place your other hand on top of the first. Interlock your fingers.
  • With straight arms, use the heel of your hand to push the breastbone down firmly and smoothly, so that the chest is pressed down between 5 to 6cm, and release.

Do this at a rate of 100 to 120 chest compressions per minute – that’s around 2 per second.

Step 5:  Keep going

  • Keep going until professional help arrives and takes over, or the person starts to show signs of regaining consciousness, such as coughing, opening their eyes, speaking, or breathing normally.

If you’re feeling tired and there’s someone nearby to help, instruct them to continue.

What causes a cardiac arrest?

A common cause of a cardiac arrest is a life-threatening abnormal heart rhythm called ventricular fibrillation (VF).

VF happens when the electrical activity of the heart becomes so chaotic that the heart stops pumping. Instead, it quivers or ‘fibrillates’.

The main causes of cardiac arrest related to a heart condition are:

  • A heart attack (caused by coronary heart disease)
  • Cardiomyopathy and some inherited heart conditions
  • Congenital heart disease
  • Heart valve disease
  • Acute myocarditis 
    (inflammation of the heart muscle).

Some other causes of cardiac arrest include:

  • Electrocution
  • A drug overdose
  • A severe haemorrhage (known as hypovolaemic shock) – losing a large amount of blood
  • Hypoxia – caused by a severe drop in oxygen levels.

What’s the difference between a cardiac arrest and a heart attack?

A heart attack and cardiac arrest are not the same.

A heart attack happens when the blood supply to the heart muscle is cut off. This is often caused by a clot in one of the coronary arteries. The heart is still pumping blood around the body during a heart attack. The person will be conscious and breathing.

A heart attack can lead to a cardiac arrest. It’s vitally important to get medical attention immediately by calling 999 for an ambulance if you experience heart attack symptoms. 


How is a cardiac arrest treated?

Starting immediate CPR is vital as it keeps blood and oxygen circulating to the brain and around the body. A defibrillator will then deliver a controlled electric shock to try and get the heart beating normally again.

Public access defibrillators are often in locations like train stations and shopping centres. Anyone can use one and you don’t need training to do so. 

If you’re with someone who’s having a cardiac arrest, call 999, start CPR and use a defibrillator if there’s one nearby. Follow instructions from the 999 operator until emergency services take over.

Recovery after a cardiac arrest

Immediate recovery

After a cardiac arrest, you’ll have been looked after in a coronary care or intensive care unit. You may have been put in an induced coma and kept asleep to allow your body to recover.

Mid-term recovery

Doctors and cardiologists will want to work out what caused the cardiac arrest. They can then recommend medication and treatment, such as a pacemaker or implantable cardioverter defibrillator (ICD), to reduce the risk of it happening again.

They may also refer you to cardiac rehabilitation to help rebuild your confidence, fitness and strength levels. Each programme is different, but it usually involves regular assessments such as checking your pulse and blood pressure, psychological support, health education talks and exercise sessions.

Long-term recovery

It will take time to recover after a cardiac arrest, but your doctor will support you during this time. Talk to family and doctors about what will happen once you go home and practical matters, such as driving and returning to work.
Your doctor may suggest making lifestyle changes to reduce your risk of another cardiac arrest. This can include:
  • Eating a healthy diet
  • Quitting smoking
  • Cutting down on alcohol
  • Being physically active

Because of the lack of oxygen to the brain during a cardiac arrest, you might experience long-term effects to you brain.


These can include:

  • Personality changes
  • Problems with memory
  • Fatigue
  • Dizziness or balance issues
  • Aphasia/dysphasia (problems with speech and language)
  • Myoclonus (involuntary movements)
  • Permanent brain injury

It’s normal to have no memory of a cardiac arrest. This can be alarming for you and your family members who may have seen it happen.