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Cardiac arrest

11-minute read

If someone near you has lost consciousness and isn’t breathing normally, call triple zero (000) immediately and ask for an ambulance. In the meantime, start CPR and follow all instructions given by the triple zero (000) operator.

Key facts

  • A cardiac arrest is when the heart stops beating, stopping blood flow to the brain and body.
  • It is usually caused by an electrical problem with the heart, while a heart attack is caused by a blockage in the blood vessels that supply the heart.
  • Prompt cardiopulmonary resuscitation (CPR) and defibrillation (controlled electric shock) increase the chance of surviving a cardiac arrest.

What is cardiac arrest?

A cardiac arrest is when the heart suddenly stops beating. This means that the blood flow to the brain and body organs stops, and the body becomes starved of oxygen. If a cardiac arrest is not treated quickly, it will usually be fatal.

Some people in hospital experience a cardiac arrest because of a medical condition. This article will cover the symptoms and treatment of a cardiac arrest that occurs suddenly.

What is the difference between a cardiac arrest and a heart attack?

Cardiac arrest is not the same as a heart attack.

During a heart attack (also known as an acute myocardial infarction or AMI), a blockage in the coronary arteries stops enough blood getting to the heart muscle. Left untreated, the heart muscle may start to die from lack of oxygen.

During a sudden cardiac arrest, a problem with the heart’s electrical conduction system causes it to stop beating properly.

See the table below for the main differences between a cardiac arrest and a heart attack.

Cardiac arrest

Heart attack



May develop gradually over minutes or hours


The person will usually collapse and stop breathing normally

The person will usually remain conscious and breathing


An electrical conduction problem in the heart, stopping blood flow to the brain and organs

A blockage in the coronary arteries, restricting blood flow to the heart


Defibrillation to restore the heart’s rhythm

Medicines or surgery to remove or bypass the blockage

What causes a cardiac arrest?

A sudden cardiac arrest occurs due to a problem with the electrical conduction system of the heart that causes it to beat irregularly and ineffectively or stop beating altogether.

Sudden cardiac arrest is most commonly due to cardiac (heart) problems including:

Cardiac arrest can also be caused by non-cardiac medical problems, known as ‘secondary cardiac arrest’. It can be caused by:

  • electrolyte imbalances in the blood (such as sodium or potassium levels that are too high or too low)
  • pulmonary embolism (blood clot in the lung)
  • pneumothorax (collapsed lung)
  • drug or alcohol use
  • drug or medicine overdose
  • hypoxia (severe lack of oxygen)
  • hypothermia (low core body temperature)

Most non-cardiac causes of cardiac arrest come on gradually and usually cause symptoms before the person collapses. Some people with these problems may already be in hospital.

What are the symptoms of cardiac arrest?

Cardiac arrests outside of hospital usually occur suddenly and without warning. A person with cardiac arrest will:

  • fall unconscious
  • have no pulse
  • not be breathing normally

 Sometimes, there may be warning signs before a cardiac arrest, such as:

When should I call an ambulance?

If you or someone else has severe chest pain, shortness of breath or has lost consciousness, call triple zero (000) immediately and ask for an ambulance. In the meantime, if the person isn’t breathing normally, start CPR and follow all instructions given by the triple zero (000) operator.

How is cardiac arrest treated?

If you think someone has had a cardiac arrest:

  1. Call triple zero (000) and ask for an ambulance. Follow all instructions given by the triple zero (000) operator.
  2. Start cardiopulmonary resuscitation (CPR).
  3. If a defibrillator (known as an automated external defibrillator or AED) is available, turn it on and follow the instructions given by the device.

It is important that a cardiac arrest is treated as quickly as possible. The quicker blood flow and oxygen can be restored to the brain, the lower the chance that the person will suffer brain damage, if they recover. However, it’s important to remember that only defibrillation (delivering a controlled electric shock) can treat the cause of a cardiac arrest by restarting the heart.

Untreated cardiac arrest can be fatal — it’s always best to try resuscitation.

Learn how to perform CPR.

Watch this video from St John Ambulance, WA to learn how to treat a cardiac arrest.

Automated external defibrillator

An AED is a small, portable device designed to give a controlled electric shock to someone in cardiac arrest.

AEDs are available in many public locations, including schools, shopping centres and sports venues. They are designed to be used by anyone, even people without medical training.

Learn more about using an AED.

Can I recover from cardiac arrest?

If someone is in cardiac arrest for longer than a few minutes, there is a chance that they will develop brain damage, which may be severe. The quicker a cardiac arrest is identified and treated, the higher the chance of a full recovery.

Factors that influence the chance of a full recovery following a cardiac arrest include:

  • the amount of time between the person’s collapse and start of CPR and/or defibrillation
  • the quality of CPR and defibrillation given
  • how long it took for brain activity to be restored following the cardiac arrest

Can cardiac arrest be prevented?

Some causes of cardiac arrest cannot be prevented, but there are things that you can do to reduce your chance of developing conditions that increase your risk.

Here are some tips to maintain optimal heart health:

Resources and support

  • The Heart Foundation has support and information on cardiac arrest and heart health.
  • Heart of the Nation is a non-profit organisation involved in public awareness and education to manage cardiac arrest in the community.

Other languages

Do you prefer to read languages other than English? The Heart Foundation has fact sheets on heart health translated into more than 25 languages.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: February 2024

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