If someone has collapsed right now
If they are unresponsive and not breathing normally, this is cardiac arrest. Call 108 and start chest compressions immediately — push hard and fast in the centre of the chest, about twice per second, and do not stop until help arrives. Doing something imperfectly is vastly better than doing nothing.
The short answer
A heart attack is a plumbing problem: an artery supplying the heart muscle is blocked. The person is usually conscious and in pain.
Cardiac arrest is an electrical problem: the heart stops pumping effectively altogether. The person collapses, is unresponsive, and is not breathing normally.
A heart attack can cause cardiac arrest. Cardiac arrest is the more immediately life-threatening of the two.
What a heart attack is
A clot forms in one of the coronary arteries, cutting off blood supply to part of the heart muscle. That muscle begins to die. The person typically has chest pain or pressure, breathlessness, sweating and nausea — and they are awake and able to tell you about it.
Treatment is aimed at reopening the artery quickly, usually with angioplasty. The person needs to get to a hospital fast, but they are conscious and their heart is still beating.
Read more on heart attack symptoms.
What cardiac arrest is
The heart's electrical rhythm becomes chaotic, or stops. The heart no longer pumps blood, so the brain is starved of oxygen within seconds. The person collapses without warning, does not respond, and either does not breathe or takes occasional gasping breaths.
There is no window for deliberation here. Without chest compressions, the chance of survival falls with every minute that passes. Treatment is CPR and, where available, a defibrillator to shock the heart back into a normal rhythm.
How they connect
A heart attack is one of the commonest triggers for cardiac arrest — damaged heart muscle can generate a dangerous rhythm. But they are not the same, and neither always causes the other:
| | Heart attack | Cardiac arrest | | --- | --- | --- | | Cause | Blocked artery | Electrical failure | | Conscious? | Usually yes | No | | Breathing? | Yes | No, or gasping only | | First response | Call 108, get to hospital | Call 108, start CPR now | | Hospital treatment | Reopen the artery | Restart the rhythm, then find the cause |
What to do in each case
If someone has chest pain but is conscious: call 108, sit them down, loosen tight clothing, give aspirin to chew if it is available and they are not allergic, and do not let them drive.
If someone has collapsed and is unresponsive: shout for help, call 108, and start chest compressions in the centre of the chest immediately. If an automated defibrillator is available, use it — the instructions are spoken aloud and designed for people with no training.
Do not spend time checking for a pulse. If they are unresponsive and not breathing normally, act.
Learning CPR is the single most useful thing
Survival from cardiac arrest outside hospital depends overwhelmingly on whether a bystander starts compressions before the ambulance arrives. It is a skill that takes a couple of hours to learn and can be used on a relative, a colleague or a stranger.
If you have a family member with known heart disease, learning it is one of the more consequential things you can do for them.
This page is general health information, not medical advice. It cannot account for your history, medication or test results. Please speak to a qualified doctor about your own symptoms and treatment. If you think you are having a medical emergency, seek immediate help.