The chain of survival is the sequence of actions that, when carried out quickly and in order, gives a person the best possible chance of surviving a sudden cardiac arrest. Each link in the chain matters. A break anywhere — a delay in recognition, a bystander who doesn’t act, a defibrillator that can’t be found — reduces the chance of survival. Every link strengthened improves it.
In the UK, around 30,000 people a year receive resuscitation attempts for an out-of-hospital cardiac arrest. Fewer than one in ten survive to leave hospital. That figure is not fixed — countries with higher rates of bystander CPR and public access defibrillation achieve significantly better outcomes. The chain of survival is why.
The four links
- Early recognition and call for help
- Early CPR
- Early defibrillation
- Post-resuscitation care and recovery
Link 1 — Early recognition and call for help
The first link is recognising that someone is in cardiac arrest and calling 999 immediately. Speed matters because brain injury begins within minutes of the heart stopping. Every second without blood flow to the brain makes survival and meaningful recovery less likely.
When you call 999, the operator will ask two key questions: is the person conscious, and are they breathing normally? If the answer to both is no, cardiac arrest is assumed and help is dispatched. The operator will guide you through what to do until paramedics arrive.
One complication at this stage is agonal breathing — the irregular gasping that can occur in the early moments of cardiac arrest. It is not normal breathing. It does not mean the heart is pumping. It is often mistaken for a sign of life, which causes dangerous delays in starting CPR. If someone collapses suddenly and is unresponsive, treat it as a cardiac arrest and call 999 immediately, regardless of whether they appear to be making any breathing effort.
Prevention also sits in this first link — recognising the warning signs of conditions that can lead to cardiac arrest, such as a heart attack, and acting before arrest occurs.
Link 2 — Early CPR
CPR — cardiopulmonary resuscitation — keeps oxygenated blood moving to the brain while the heart is not beating. It buys time. It does not restart the heart on its own, but it maintains brain function until defibrillation or advanced care can do so. Without it, brain damage becomes irreversible within minutes.
Bystander CPR — performed by whoever is present before paramedics arrive — is one of the most powerful determinants of survival. In countries like Norway, where bystander CPR rates exceed 70%, survival rates are dramatically higher than in the UK. In the UK, fewer than half of cardiac arrests receive bystander CPR.
Hands-only CPR — hard, fast compressions in the centre of the chest at 100–120 beats per minute — is the recommended approach for untrained bystanders and is as effective as CPR with rescue breaths in the first few minutes of a witnessed arrest. The British Heart Foundation’s RevivR tool can teach anyone the basics in 15 minutes. Learning CPR is one of the most impactful things a person can do.
Link 3 — Early defibrillation
CPR maintains circulation but in most cases only a defibrillator shock can restore a normal heart rhythm. The most common cause of cardiac arrest is ventricular fibrillation — a chaotic electrical rhythm that prevents the heart from pumping — and defibrillation is the only effective treatment for it. For every minute without defibrillation, survival rates fall by approximately 10%.
Automated external defibrillators (AEDs) are designed for use by anyone, with no training required. They analyse the heart rhythm and only deliver a shock if one is needed — you cannot accidentally shock a heart that doesn’t need it. They talk you through every step. They are increasingly available in public places: shopping centres, train stations, sports facilities, workplaces, schools, and community settings.
When you call 999 for a cardiac arrest, the operator will tell you the location of the nearest AED. Finding one and using it before the ambulance arrives can be the difference between life and death. You can also find your nearest AED using our AED map.
As public access AED pioneer Professor Douglas Chamberlain famously said: “The only damage you can do to someone with an AED is if you whack them round the head with it.”
Link 4 — Post-resuscitation care and recovery
The fourth link covers everything that happens after return of spontaneous circulation (ROSC) — the point at which the heart starts beating again. This includes stabilisation in hospital, investigation of the underlying cause, intensive care, and the long process of physical and psychological recovery that follows discharge.
This link is frequently the least developed. Unlike the acute steps, recovery after cardiac arrest can take months or years, and the challenges survivors face — fatigue, memory difficulties, anxiety, PTSD, practical issues around driving and returning to work — are often poorly supported by clinical services.
This is the link that SCA UK exists to strengthen. The Resuscitation Council UK, the European Resuscitation Council, and the American Heart Association have all now formally recognised that the chain of survival must extend through long-term survivorship — not end at hospital discharge.
The chain and co-survivors
Most cardiac arrests happen at home. The person who calls 999, starts CPR, and finds the AED is typically a family member, partner, colleague, or bystander — not a medical professional. These people are the chain of survival. Without them, the later links rarely get the chance to work.
Being part of a resuscitation attempt — even a successful one — can be deeply traumatic. Many co-survivors experience anxiety, PTSD, and lasting psychological effects from what they witnessed and did. Their needs are real and too often go unmet. If you have given CPR or witnessed a cardiac arrest, you are not alone. Support is available through our co-survivor community and through Chain of Survival UK, our dedicated community for co-survivors.
Strengthening every link
The chain of survival is only as strong as its weakest link. In the UK, the weakest links are bystander CPR rates and public AED use — both of which are determined by public awareness and training. The more people who know what cardiac arrest looks like, who are confident performing CPR, and who know where their nearest AED is, the more lives are saved.
You can strengthen the chain by learning CPR — it takes 15 minutes online with the BHF’s RevivR tool — and by knowing where your nearest AED is located. If your workplace, school, or community venue doesn’t have one, consider advocating for one.
If you or someone you love has survived a cardiac arrest, the fourth link in the chain is now your territory. Our community of thousands of survivors and co-survivors understands what life after cardiac arrest is like. Join SCA UK to connect with people who have been through it — and find the support that the chain of survival too rarely provides.