Cardiac arrest

Person performing chest compressions

A cardiac arrest happens when your heart stops pumping blood around your body.

If someone has suddenly collapsed, is not breathing normally and is unresponsive, they are in cardiac arrest.

There is no time to lose. Even if you are untrained your actions can help.

A cardiac arrest is an emergency.  If you witness a cardiac arrest, you can increase the person’s chances of survival by phoning 999 immediately and giving CPR.

CPR means:
  • chest compression (pumping the heart by external cardiac massage), to keep the circulation going until the ambulance arrives and
  • rescue breathing (inflating the lungs by using mouth-to-mouth resuscitation).
Remember - even if you haven't been trained in CPR with rescue breathing, you can still use hands-only CPR.

Learn CPR

What causes a cardiac arrest?

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

Ventricular fibrillation happens when the electrical activity of your heart becomes so chaotic that the heart stops pumping and quivers or 'fibrillates' instead. There are various causes of VF. These can be problems with your heart, or other causes.

Heart-related causes of VF
Other causes of VF

Coronary heart disease

A lack of oxygen in your body - for example, if you are choking

Heart attack



Using recreational drugs, such as cocaine

Congenital heart disease

Losing a large amount of blood

Heart valve disease


Acute Myocarditis (inflammation of the heart muscle)


Heart conduction disorders that make you more likely to experience abnormal heart rhythms, such as Long QT syndrome


Can you recover from a cardiac arrest?

DefibrillatorIt is possible to survive and recover from a cardiac arrest, if you get the right treatment quickly.

VF can sometimes be corrected by giving an electric shock through the chest wall, by using a device called a defibrillator.

This can be done in the ambulance, or at hospital, or it can be done by a member of the public at the scene of a cardiac arrest if there is a community defibrillator nearby.

Immediate CPR can be used to keep oxygen circulating around the body until a defibrillator can be used and/or until the ambulance arrives.

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

Although a heart attack can lead to a cardiac arrest, they are not the same thing.

A cardiac arrest happens when your heart stops pumping blood around your body. A heart attack happens when when your heart muscle is starved of oxygen-rich blood. A cardiac arrest does not always happen because you have a heart condition, although this can be one of the causes.

Someone who is having, or has had, a cardiac arrest will have stopped breathing normally and will be unconscious. Someone who is having or has had a heart attack will still be conscious and will be breathing, unless their heart attack has led to a cardiac arrest.

Both a heart attack and a cardiac arrest are life-threatening. If you witness a cardiac arrest or a heart attack, you should always call 999 immediately.