Cardiac Arrest vs Heart Attack — What’s the Difference?
Most people use these terms interchangeably. They are completely different emergencies — and knowing the difference could save a life.
A heart attack is a circulation (plumbing) problem: a blocked artery starves part of the heart muscle of oxygen, but the person is usually conscious and still breathing. Call 911, help them rest, and give aspirin if they can take it.
A cardiac arrest is an electrical problem: the heart suddenly stops pumping, so the person collapses, is unresponsive, and is not breathing normally. Call 911, start CPR immediately (push hard and fast in the centre of the chest at 100–120/min, at least 5 cm deep), and use an AED as soon as one arrives. A heart attack can lead to cardiac arrest, so both are 911 emergencies.
A fundamental misunderstanding persists: most people think “heart attack” and “cardiac arrest” mean the same thing. They do not. Confusing them can delay the right response and cost precious minutes.
Here is the clearest way to understand the difference: a heart attack is a plumbing problem. Cardiac arrest is an electrical problem. Both are emergencies. Both can kill. But they require very different responses.
Heart Attack: A Circulation Problem
A heart attack (myocardial infarction) happens when a blocked artery prevents blood from reaching part of the heart muscle. The blockage is usually caused by a blood clot forming on a build-up of fatty deposits (plaque) inside a coronary artery. The heart is still beating, but part of it is being starved of oxygen. The longer the blockage persists, the more heart muscle dies.
Heart Attack Symptoms
- Chest pain or pressure — often described as a squeezing, tightness, or heaviness in the centre of the chest. It may come and go.
- Pain radiating to the arms, neck, jaw, or back — most commonly the left arm, but it can affect both arms or the jaw
- Shortness of breath — with or without chest discomfort
- Nausea, lightheadedness, or cold sweats
- Unusual fatigue — particularly in women, who may experience fatigue for days before the event
Symptoms per Heart & Stroke Foundation of Canada and Canadian Red Cross first aid guidance (2025).
What to Do for a Heart Attack
- Call 911 immediately — do not drive the person to the hospital yourself unless there is absolutely no other option
- Help them sit in a comfortable position — usually sitting up and leaning slightly forward. This makes breathing easier.
- Give aspirin — if the person is not allergic and can swallow, have them chew one adult (325 mg) aspirin, or the equivalent as low-dose (81 mg) tablets. Chewed aspirin helps stop the clot from growing. (Heart & Stroke Foundation of Canada / Canadian Red Cross.)
- Keep them calm — reassure them that help is on the way. Anxiety increases the heart’s workload.
- Monitor them continuously — if they become unresponsive and stop breathing normally, they have gone into cardiac arrest. Begin CPR immediately.
Source: Heart & Stroke Foundation of Canada; Canadian Red Cross first aid guidance (2025). Aspirin only if not contraindicated — follow the 911 dispatcher’s instructions.
Cardiac Arrest: An Electrical Problem
Cardiac arrest is the sudden, unexpected loss of heart function. The heart’s electrical system malfunctions, causing it to quiver chaotically (ventricular fibrillation) or stop entirely. Blood stops flowing to the brain and organs. Without intervention, death occurs within minutes.
The key difference: during a heart attack, the person is conscious and their heart is beating. During cardiac arrest, the person is unconscious, not breathing normally, and their heart has effectively stopped pumping blood.
What to Do for Cardiac Arrest
- Recognise it — the person collapses, is unresponsive, and is not breathing or is only gasping. (Occasional gasping is not normal breathing.)
- Call 911 — or point at a specific person and have them call while you start CPR. Put the phone on speaker.
- Begin CPR immediately — push hard and fast in the centre of the chest (the lower half of the breastbone) at a rate of 100 to 120 compressions per minute, at least 5 cm deep, letting the chest come all the way back up between pushes. Do not stop. (Canadian Red Cross / Heart & Stroke, per ILCOR 2025 BLS.)
- Use an AED — send someone to get the nearest automated external defibrillator. Turn it on and follow the voice prompts. The AED analyses the heart rhythm and advises a shock only if one is needed. Learn how to use an AED.
- Continue CPR until paramedics arrive — do not stop compressions except to deliver AED shocks when prompted
Source: Canadian Red Cross 2025; Heart & Stroke Foundation (ILCOR 2025 BLS). Compression rate 100–120/min; depth at least 5 cm (and no more than 6 cm); hand position on the lower half of the sternum.
Side-by-Side Comparison
| Feature | Heart Attack | Cardiac Arrest |
|---|---|---|
| What happens | Blocked artery reduces blood flow to heart muscle | Heart’s electrical system fails; heart stops pumping |
| Consciousness | Person is conscious and alert | Person is unconscious and unresponsive |
| Breathing | Person is breathing (may be laboured) | Person is not breathing or only gasping |
| Pulse | Pulse is present | No effective pulse |
| Onset | Symptoms can develop over minutes to hours | Sudden collapse without warning |
| First aid | Call 911, aspirin, comfortable position, monitor | Call 911, CPR immediately, use AED |
| CPR needed? | Only if the person goes into cardiac arrest | Yes — immediately and continuously |
The Connection Between the Two
A heart attack can trigger cardiac arrest. When heart muscle is damaged by a blocked artery, the disruption can cause the heart’s electrical system to malfunction. This is why heart attacks are time-critical emergencies — rapid treatment to open the blocked artery reduces the risk of cardiac arrest.
However, cardiac arrest can also happen without a heart attack. Other causes include drowning, drug overdose, severe blood loss, electric shock, and underlying heart conditions that the person may not even know they have.
Why CPR Training Matters for Both
Understanding the difference between these emergencies is important, but the practical skill that saves lives is CPR. In a Life Safe CPR course, you learn to recognise both conditions, respond appropriately, and — when cardiac arrest strikes — deliver effective chest compressions that keep blood flowing to the brain until paramedics arrive.
Life Safe’s CPR Coach app gives you real-time feedback on your compression depth, rate, and consistency during training, so you know — not just hope — that your CPR is effective.
Frequently Asked Questions
Can a heart attack cause cardiac arrest?
Yes. A heart attack can trigger cardiac arrest, which is one of the reasons heart attacks are so dangerous. When blood flow to the heart muscle is blocked during a heart attack, the resulting damage can disrupt the heart’s electrical system and cause it to stop beating effectively. This is why it is critical to call 911 immediately for heart attack symptoms — rapid treatment reduces the risk of cardiac arrest.
Do you perform CPR during a heart attack?
Not unless the person goes into cardiac arrest. During a heart attack, the person is conscious and their heart is still beating. Help them sit in a comfortable position, call 911, and give them aspirin if they are not allergic. If at any point the person becomes unresponsive and stops breathing normally, that is cardiac arrest — begin CPR immediately and use an AED if available.
What are the signs of a heart attack in women?
Women may experience the classic chest pain or pressure, but they are more likely than men to have atypical symptoms: shortness of breath, nausea or vomiting, back or jaw pain, unusual fatigue, lightheadedness, and discomfort in one or both arms. These less obvious symptoms are one reason heart attacks in women are more often missed or delayed. Any combination of these symptoms warrants calling 911.
How effective is bystander CPR for cardiac arrest?
Extremely effective. According to the Heart & Stroke Foundation, bystander CPR can double or even triple the chance of surviving an out-of-hospital cardiac arrest. When CPR is combined with early defibrillation using an AED, survival improves further. Without any bystander intervention, survival from out-of-hospital cardiac arrest is low — often under 10 percent.
Can young people have cardiac arrest?
Yes. While cardiac arrest is more common in older adults, it can happen to young people — including athletes and children — often due to undiagnosed heart conditions such as hypertrophic cardiomyopathy or electrical abnormalities like long QT syndrome. Sudden cardiac arrest in young athletes, while rare, is one of the leading causes of death during sports. This is why AEDs in schools and sports facilities are so important.
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, and the 2025 ILCOR Basic Life Support consensus. Last reviewed July 2026.