Sudden Cardiac Arrest: What Every Bystander Should Know
Sudden cardiac arrest is one of Canada’s leading causes of death. A bystander who acts in the first minutes is the victim’s best chance of survival.
If someone collapses, is unresponsive, and is not breathing normally, treat it as sudden cardiac arrest and act fast: (1) check the scene is safe; (2) call 911 (on speakerphone) or send someone to call and to find an AED; (3) start CPR immediately — push on the lower half of the breastbone, at least 5 cm deep (no more than 6 cm) at 100–120 compressions/min, letting the chest recoil fully; (4) use the AED as soon as it arrives and follow its voice prompts. Untrained? Do hands-only compressions and let the 911 dispatcher coach you.
Sudden cardiac arrest (SCA) is the abrupt loss of heart function. Within seconds, the person loses consciousness and stops breathing normally. Without immediate intervention, brain cells begin dying in four to six minutes and are usually lost by about eight to ten minutes. It is not the same as a heart attack — and confusing the two costs lives.
Source: Canadian Red Cross, 2025 (First Aid & CPR manual) — brain injury window and mechanism of arrest.
Tens of thousands of Canadians experience an out-of-hospital cardiac arrest every year, and survival is low: overall survival for out-of-hospital cardiac arrest is commonly reported at around 10–12%. But where bystanders act quickly — starting CPR and using an AED within the first few minutes — reported survival is dramatically higher. The gap between those numbers is you.
Cardiac Arrest vs Heart Attack: The Critical Difference
| Heart Attack | Cardiac Arrest | |
|---|---|---|
| What it is | A blocked artery reduces blood flow to part of the heart muscle (a circulation problem) | The heart’s electrical system malfunctions and the heart stops pumping effectively (an electrical problem) |
| Is the person conscious? | Usually yes — they may be alert and talking | No — they lose consciousness within seconds |
| Are they breathing? | Yes, though breathing may be laboured | Not normally — may gasp (agonal breathing) but not truly breathing |
| Symptoms | Chest pain/pressure, pain radiating to arm/jaw/back, shortness of breath, nausea, cold sweat | Sudden collapse, no pulse, no normal breathing, unresponsive |
| What to do | Call 911. Keep the person calm and still. Aspirin may be advised for a suspected heart attack — give it only if the person is not allergic and it is not contraindicated, ideally as directed by 911 | Call 911. Start CPR immediately. Use an AED as soon as one is available |
Source: Canadian Red Cross / Heart & Stroke Foundation, 2025. Aspirin for suspected heart attack: Heart & Stroke / Canadian Red Cross — only when not contraindicated.
The Chain of Survival
Survival from cardiac arrest depends on a chain of events, each link increasing the chance of a positive outcome. Break one link, and survival drops dramatically:
- Early recognition and call to 911 — identify cardiac arrest (unresponsive, no normal breathing) and activate emergency medical services immediately
- Early CPR — bystander chest compressions keep oxygenated blood circulating to the brain and heart. Push hard (at least 5 cm deep, no more than 6 cm), push fast (100–120 per minute), and do not stop
- Early defibrillation — an AED delivers a shock that can restore a normal heart rhythm. For every minute without CPR and defibrillation, the chance of survival drops by roughly 7–10%
- Early advanced care — paramedics provide medications, advanced airway management, and transport to hospital
Source: Heart & Stroke Foundation / AHA 2025 Chain of Survival; 7–10%-per-minute decay and rate/depth per Canadian Red Cross, 2025 (aligned with ILCOR 2025 BLS).
How to Respond to Sudden Cardiac Arrest
- Check the scene — ensure it is safe to approach
- Check the person — tap their shoulders and shout “Are you okay?” If there is no response and no normal breathing, treat it as cardiac arrest. Occasional gasping (agonal breathing) is not normal breathing
- Call 911 — or have someone else call while you start CPR. Put the phone on speaker
- Start CPR immediately — place the heel of one hand on the lower half of the breastbone in the centre of the chest, place the other hand on top and interlock your fingers, and push hard and fast. 100–120 compressions per minute, at least 5 cm deep (no more than 6 cm). Let the chest fully recoil between compressions
- Send someone for an AED — many public buildings, arenas, schools, and workplaces have them. When the AED arrives, turn it on and follow the voice prompts — it will tell you exactly what to do
- Continue CPR until the AED is ready, the person starts responding, or paramedics take over
Source: Canadian Red Cross, 2025 (rate 100–120/min; depth at least 5 cm, not more than 6 cm; lower half of the sternum); aligned with ILCOR 2025 BLS & ERC 2025 BLS.
Cardiac Arrest in Children
While cardiac arrest in children is less common than in adults, it does happen — and the causes are often different. In children, cardiac arrest is more frequently caused by a breathing problem first (choking, drowning, asthma) rather than a primary heart problem. Because the underlying problem is a lack of oxygen, rescue breaths matter more in paediatric CPR, and hands-only CPR is not enough for a child.
Source: Canadian Red Cross, 2025 — paediatric arrest is usually respiratory in origin.
For children and infants, a single (lay) rescuer uses 30 compressions to 2 breaths, at 100–120 per minute. Compress at least one-third the depth of the chest (a fraction, not a fixed number, because children range from newborns to nearly adult-sized).
- Child (1 yr–puberty): use one or two hands on the centre of the chest.
- Infant (under 12 months): use the two-thumb encircling technique, or the heel of one hand, on the lower half of the breastbone. The older two-finger method is no longer the recommended technique.
If you are not trained in rescue breaths, hands-only compressions are still far better than doing nothing.
Source: American Heart Association (AHA) 2025 — two-finger infant technique retired in favour of two-thumb encircling or heel of one hand; depth ≥⅓ chest, rate 100–120/min per Canadian Red Cross, 2025. See our baby CPR guide.
Where to Find an AED
AEDs are increasingly available in public spaces across Ontario — look for them in shopping malls, community centres, arenas, airports, gyms, schools, office buildings, and some condo lobbies. They are typically housed in a bright red or green wall cabinet with a heart symbol. Many municipalities maintain a public AED registry — check your local public health unit’s website. Remember: anyone can use an AED — no training is needed, and you should use it as soon as it arrives.
Source: European Resuscitation Council (ERC) 2025 BLS — anyone can use an AED, no training required; use as soon as available.
Frequently Asked Questions
What is sudden cardiac arrest?
Sudden cardiac arrest is the abrupt loss of heart function caused by an electrical malfunction in the heart. The heart stops pumping effectively, blood stops flowing to the brain and organs, and the person loses consciousness within seconds. Without CPR and defibrillation within minutes, it is fatal. It is different from a heart attack, which is a circulation problem caused by a blocked artery.
Can sudden cardiac arrest happen to young, healthy people?
Yes. While the risk increases with age and heart disease, sudden cardiac arrest can occur in seemingly healthy people of any age, including children and young athletes. In younger people, it may be caused by undiagnosed heart conditions such as hypertrophic cardiomyopathy, electrical abnormalities like Long QT syndrome, or commotio cordis (a blow to the chest at a critical moment in the heartbeat cycle).
How long do you have to start CPR after cardiac arrest?
Brain damage begins within four to six minutes without oxygenated blood, and is usually irreversible by about eight to ten minutes (Canadian Red Cross, 2025). For every minute that CPR and defibrillation are delayed, the chance of survival drops by roughly 7–10%. This is why immediate bystander CPR is so critical — every second before help arrives matters.
Can a regular person use an AED?
Yes. AEDs are designed for use by anyone, with no training needed (ERC 2025). When you turn on the device, it provides clear voice instructions and visual prompts. It analyses the heart rhythm automatically and will only deliver a shock if it detects a rhythm that can be corrected by defibrillation, so you cannot accidentally shock someone who does not need it. Training helps you act faster and more confidently, but the device itself is very user-friendly.
What is the survival rate for cardiac arrest?
The overall survival rate for out-of-hospital cardiac arrest in Canada is low — commonly reported at around 10–12%. However, when bystanders perform CPR immediately and an AED is used within the first few minutes, reported survival rates are far higher. The difference is bystander action — which is why CPR and AED training saves lives.
Sources & medical review
Written and reviewed by Milos Radojcic (Canadian Red Cross / Heart & Stroke / Lifesaving Society First Aid & CPR Instructor, 10+ yrs; First Aid Instructor Trainer). Clinical content aligned with the Canadian Red Cross (2025), the Heart & Stroke Foundation of Canada, the American Heart Association (AHA) 2025 guidelines, and the 2025 ILCOR international Basic Life Support consensus. Last reviewed July 2026.