Heart Attack or Cardiac Arrest: Key Differences

A heart attack, or myocardial infarction, happens when a coronary artery becomes blocked, usually by a clot forming on a fatty plaque. The heart muscle keeps contracting, but part of its cells lose oxygen and start to suffer. The person stays conscious, keeps breathing and still has a pulse, even if the pain can be severe.

Cardiac arrest, or more precisely cardiopulmonary arrest, is a sudden stop of the heart's electrical activity, most often a ventricular fibrillation. The heart stops pumping blood, the person loses consciousness within seconds and stops breathing normally. Without immediate intervention, brain damage sets in within minutes.

The signs of a heart attack often build up gradually: a tight, oppressive pain in the centre of the chest, which can spread to the left arm, the jaw or the back, along with sweating, nausea or shortness of breath. The person stays awake and can describe what they feel. Cardiac arrest, by contrast, shows up as a sudden loss of consciousness: the person collapses, stops responding and stops breathing normally, or breathes in an irregular, gasping way with long pauses between breaths.

When in doubt, it is safer to act as if it were a cardiac arrest: check for a response by speaking loudly and tapping the shoulders, watch the chest for a few seconds to check breathing, and call emergency services straight away if the person does not respond or breathes abnormally.

The confusion largely comes from the fact that a heart attack can turn into a cardiac arrest. The lack of oxygen in the heart muscle destabilises its electrical activity and can trigger ventricular fibrillation at any moment, including within minutes of the first symptoms. A poorly managed heart attack is in fact one of the main causes of cardiac arrest in adults.

This shift explains why vigilance still matters even when the person seems stable after the first signs. A bystander should never leave someone who has just described chest pain while waiting for help, since their condition can worsen very quickly.

Facing signs of a heart attack, the priority is to call emergency services without waiting for the pain to ease, to have the person rest in a semi-sitting position and to avoid giving them anything to eat or drink. The medical dispatcher takes over from there and can send a team able to unblock the artery quickly.

Facing a cardiac arrest, the timeline changes: call emergency services, start chest compressions immediately by pressing hard and fast in the centre of the chest, and ask another bystander to fetch a nearby defibrillator. Every minute without defibrillation lowers the chances of survival by around 10 percent, which makes alternating between compressions and placing the pads decisive.

An automated external defibrillator (AED) reads the heart's rhythm and only delivers a shock if it detects ventricular fibrillation or pulseless ventricular tachycardia, the rhythms typical of cardiac arrest. Placed on someone having a heart attack while still conscious and with a pulse, the device has no reason to shock: it never replaces calling emergency services for an ongoing heart attack.

On the other hand, as soon as someone collapses, loses consciousness and stops breathing normally, the defibrillator should be brought without delay, even if the exact cause is unknown. The device gives voice guidance at every step and checks its own readings before shocking, which lets an untrained bystander use it without risking further harm.

In places that welcome the public, the best response combines training and accessible equipment: staff or volunteers able to recognise the signs, an emergency number clearly displayed and a defibrillator that is signposted and reachable at all times. This preparation does not replace professional emergency services, but it shortens the delay before the first actions, the delay that weighs most heavily on the outcome.

Regularly training staff in life saving actions, checking that the defibrillator stays operational and reminding everyone of the emergency numbers in shared spaces are simple measures that save precious time, whether the situation is a worsening heart attack or a sudden cardiac arrest.