Skip to main content

Health condition · Clinically reviewed

Cardiac arrest, an electrical emergency where minutes decide the outcome.

Not a heart attack. Cardiac arrest is the heart stopping. Early recognition, bystander CPR and a public defibrillator are the difference between life and death.

Jump to treatment
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against Resuscitation Council UK, ESC and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice including ALS 2021 guidance, TTM2 evidence and inherited cardiac conditions screening.

Key facts

Cardiac arrest at a glance.

The essentials, in plain English - what it is, how it differs from a heart attack, and how it is treated in the UK.

  • What it is

    Sudden loss of cardiac function - unresponsive, not breathing normally and no pulse. An electrical problem, not a plumbing one.

  • How common

    Around 30,000 out-of-hospital cardiac arrests each year in the UK, with fewer than 1 in 10 surviving to hospital discharge.

  • Shockable rhythms

    Ventricular fibrillation and pulseless VT - the best outcomes come with early defibrillation using a public AED.

  • Non-shockable

    Pulseless electrical activity and asystole - CPR and reversing the underlying cause are the priority.

  • Chain of survival

    Early recognition, early CPR, early defibrillation and expert post-resuscitation care - each link doubles the chance of surviving.

  • Not the same as MI

    A heart attack is a blocked artery. Cardiac arrest is the heart stopping. A heart attack can cause a cardiac arrest, but they are not the same event.

Why this guide matters

A survivable event, if the chain holds.

Fewer than one in ten survive out-of-hospital cardiac arrest in the UK. The three points below explain why the chain of survival matters so much.

  • Time is muscle and brain

    For every minute without CPR and defibrillation, survival falls by around 10 percent. Bystander action buys the ambulance time.

  • AEDs work in untrained hands

    Public defibrillators are designed for anyone to use - they will not shock unless a shockable rhythm is present. Turn it on and follow the voice prompts.

  • Post-arrest care changes outcomes

    Getting the right hospital - one that offers coronary angiography, targeted temperature management and neuroprognostication - meaningfully improves survival with good brain function.

How the emergency unfolds

From the moment of collapse to a plan for what caused it.

The steps a bystander, the ambulance crew and a UK hospital team will normally follow, in order - so you know what to expect.

  1. 01

    Resuscitate

    Recognise the collapse

    Unresponsive, not breathing or only agonal gasping, no pulse - call 999 immediately and start CPR.

  2. 02

    Resuscitate

    Bystander CPR and AED

    Hands-only chest compressions and the nearest public AED - the two things that save lives before the ambulance arrives.

  3. 03

    Resuscitate

    In-hospital arrest call

    Dial 2222 or the local arrest code. Advanced Life Support begins with rhythm check every two minutes and shocks for VF or pulseless VT.

  4. 04

    Reverse

    Reversible causes - 4H 4T

    Hypoxia, hypovolaemia, hypo or hyperkalaemia, hypothermia; tamponade, tension pneumothorax, thrombosis, toxins.

  5. 05

    Reverse

    Post-ROSC 12-lead ECG

    Return of spontaneous circulation triggers a 12-lead - urgent coronary angiography if there is any suggestion of acute coronary syndrome.

  6. 06

    Recover

    Targeted temperature management

    Controlled temperature between 32 and 36 degrees for at least 24 hours - individualised in light of TTM2 evidence.

  7. 07

    Recover

    Cause work-up and ICD review

    Echo, cardiac MRI, coronary anatomy, ambulatory ECG and inherited cardiac conditions screen where no reversible cause is found.

Typical timeline: seconds to minutes for the first three steps, hours to days for the rest.

Symptoms

What cardiac arrest actually looks like.

Unresponsive, not breathing normally, no pulse. Learn the pattern and you will not hesitate when it matters.

  • Sudden collapse

    Witnessed or unwitnessed loss of consciousness with no warning - the defining feature of cardiac arrest.

  • Unresponsive

    No response to voice or shake - do not wait to see what happens, call 999 immediately.

  • Not breathing normally

    Absent or agonal gasping breaths - noisy, irregular gasps are not normal breathing and mean cardiac arrest.

  • No pulse

    No central pulse if trained to check - but bystanders should never delay CPR to look for one.

  • Prodromal chest pain or palpitations

    Some collapse after a warning - chest pain, palpitations, breathlessness or dizziness. Many have no warning at all.

  • Seizure-like movements

    Brief jerking as the brain loses oxygen - often mistaken for a fit. Treat as cardiac arrest until proven otherwise.

  • Family history of sudden death

    Sudden death in a first-degree relative under 40 raises the possibility of an inherited cardiac condition.

  • Red flag - any collapse with no breathing

    If you cannot rouse someone and they are not breathing normally, start CPR and send for the nearest AED.

Treatment

How cardiac arrest is treated in the UK.

Bystander CPR, an AED, Advanced Life Support, treatment of the underlying cause and specialist post-resuscitation care.

  • Bystander CPR

    Hands-only chest compressions at 100 to 120 per minute in the centre of the chest - the single biggest thing a bystander can do.

  • Public-access defibrillator (AED)

    Turn it on and follow the voice prompts - a shock delivered within minutes transforms survival for VF and pulseless VT.

  • Advanced Life Support

    ALS algorithm - 30:2 compressions to breaths, rhythm check every two minutes, adrenaline 1 mg IV every 3 to 5 minutes, amiodarone 300 mg after the third shock.

  • Reversing 4H 4T

    Treat hypoxia, hypovolaemia, potassium disturbance, hypothermia, tamponade, tension pneumothorax, thrombosis and toxins alongside CPR.

  • Coronary angiography and PCI

    Urgent cath lab for post-arrest STEMI and considered in selected non-STEMI arrests with a likely cardiac cause.

  • Targeted temperature management

    Post-ROSC temperature control at 32 to 36 degrees for 24 hours, followed by careful rewarming and neurological assessment.

  • Implantable defibrillator (ICD)

    Secondary prevention for survivors without a reversible cause, and primary prevention in selected high-risk conditions.

  • Inherited cardiac conditions clinic

    Specialist review for channelopathies and cardiomyopathies, with cascade screening of first-degree relatives.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and evidence we relied on.

A quiet reminder

In an emergency, call 999. This page is not a substitute for that call.

If someone is unresponsive and not breathing normally, stop reading, call 999 and start hands-only CPR.

  • Resuscitation Council UK. Adult Advanced Life Support Guidelines 2021.

  • Resuscitation Council UK. Adult Basic Life Support and AED Guidelines 2021.

  • European Society of Cardiology. Guidelines on ventricular arrhythmias and prevention of sudden cardiac death.

  • NICE. Implantable cardioverter defibrillators and cardiac resynchronisation therapy (TA314).

  • Dankiewicz J et al. Hypothermia versus normothermia after out-of-hospital cardiac arrest (TTM2). NEJM 2021.

  • British Heart Foundation. Out-of-hospital cardiac arrest data and The Circuit defibrillator registry.

Red flags

When cardiac arrest is in the picture.

Situations that need an immediate 999 call, and features that should prompt urgent specialist assessment for arrhythmia risk.

  • Unresponsive and not breathing

    Start CPR and call 999. Ask a bystander to fetch the nearest public AED. Do not delay to check for a pulse.

  • Family history of sudden death under 40

    Raises the possibility of an inherited channelopathy or cardiomyopathy - warrants specialist assessment and cascade screening.

  • Unexplained syncope during exertion

    Fainting on exertion or with emotion can point to hypertrophic cardiomyopathy, long QT or CPVT and needs urgent cardiology review.

  • Syncope with palpitations

    Blackouts preceded by fast palpitations may reflect ventricular arrhythmia and should not be dismissed as vasovagal.

  • Post-arrest neurological changes

    Coma, seizures or myoclonus after resuscitation need specialist neuroprognostication after at least 72 hours off sedation.

  • New STEMI on post-ROSC ECG

    ST elevation after return of spontaneous circulation is an indication for urgent coronary angiography and PCI.

  • QT prolongation or Brugada pattern

    A resting ECG showing long QT or type 1 Brugada is a red flag - stop QT-prolonging drugs and refer to electrophysiology.

  • Suspected drug toxicity

    Cocaine, methamphetamine, tricyclic overdose and QT-prolonging medicines can trigger arrest - toxicology and specific antidotes matter.

  • Refractory VF

    Ventricular fibrillation that does not respond to defibrillation may need dual sequential defibrillation, mechanical CPR and ECPR in specialist centres.

Living with it

Life after a cardiac arrest, for survivors and families.

Recovery is physical, psychological and often genetic. Cardiac rehab, mental-health support, family screening and community CPR training all have their place.

A quiet reminder

Support networks matter.

Sudden Cardiac Death Charity, SADS UK, CRY UK and Cardiomyopathy UK offer specialist information, peer support and family services.

  1. 01 Recovery

    Cardiac rehabilitation

    A structured programme of supervised exercise, education and psychological support - central to recovery after any cardiac arrest.

  2. 02 Mental

    Look after your mind

    PTSD, anxiety and low mood are common in survivors and in the family who witnessed the event. Ask for help early.

  3. 03 Family

    Cascade screening

    If an inherited condition is found, first-degree relatives are offered ECG, echocardiography and genetic testing through a specialist clinic.

  4. 04 Community

    Learn CPR and know your AED

    Restart a Heart Day, workplace training and The Circuit registry help make bystander CPR and public AEDs the norm, not the exception.

Frequently asked

Everything we get asked about cardiac arrest.

Quick answers on recognition, CPR, defibrillators, causes and prevention.

  • What is a cardiac arrest?

    A cardiac arrest is the sudden loss of cardiac function - the heart stops pumping blood, the person becomes unresponsive, stops breathing normally and has no pulse. It is an electrical problem with the heart rhythm and needs immediate CPR and defibrillation.

  • How is a cardiac arrest different from a heart attack?

    A heart attack is a plumbing problem - a blocked coronary artery starving heart muscle of blood. A cardiac arrest is an electrical problem - the heart stops beating effectively. A heart attack can trigger a cardiac arrest, but they are not the same. Someone having a heart attack is usually awake and talking; someone in cardiac arrest is not.

  • What should I do if I see someone collapse?

    Check for a response. If they are unresponsive and not breathing normally, call 999 and start hands-only CPR in the centre of the chest at 100 to 120 compressions per minute. Send someone for the nearest public defibrillator. The 999 call handler will guide you.

  • Do I need to give rescue breaths?

    For untrained bystanders the current UK advice is hands-only CPR - continuous chest compressions without rescue breaths. Trained rescuers can use 30 compressions to 2 breaths. Any CPR is far better than none.

  • What causes cardiac arrest in young, apparently healthy people?

    Most cases are due to inherited cardiac conditions - hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, long QT, Brugada syndrome and CPVT. Family history of sudden death under 40 is an important clue and warrants specialist screening.

  • Why might a survivor need an implantable defibrillator?

    If no reversible cause is found for a cardiac arrest, a survivor is at high risk of another event. An implantable cardioverter defibrillator (ICD) monitors the heart and delivers a shock if a dangerous rhythm returns - the strongest evidence-based intervention for secondary prevention.

Related content

Keep reading.

Pulse Healthcare concierge

Send us your enquiry

A concierge service for UK private healthcare. We match you with the best vetted clinics and consultants in our network - they then contact you directly.

So we can match you to the right clinician close to you.

We reply to every enquiry within 24 hours (Mon–Fri). Confidential - your details are never shared outside our vetted consultant network.