What is the difference between a heart attack and a cardiac arrest?
They are different emergencies with different causes and different responses, and the terms are used interchangeably far more often than they should be. A heart attack is a circulation problem; a cardiac arrest is an electrical one.
A heart attack — medically a myocardial infarction — happens when blood flow to part of the heart muscle is blocked, usually by a clot forming on a fatty plaque in a coronary artery. The starved muscle begins to die. The person is typically conscious and breathing, and the heart is still beating.
Typical features: chest pain or pressure, which may spread to the arm, jaw, neck or back; breathlessness; sweating; nausea; and a sense of something being badly wrong. Presentation is frequently not dramatic, and can be subtler — particularly in women, older people and those with diabetes, where fatigue, indigestion-like discomfort or breathlessness may dominate. This is a documented reason for delayed treatment.
A cardiac arrest happens when the heart's electrical activity becomes chaotic or stops, so it no longer pumps. The person collapses, is unresponsive, and is not breathing normally — agonal gasping is common and is not breathing. Without intervention, death follows within minutes.
The relationship between them. A heart attack can cause a cardiac arrest, which is the most common link. But cardiac arrest also results from other causes — arrhythmias, inherited conditions, electrolyte disturbance, drowning, trauma, severe blood loss and drug effects — and can happen in people with no coronary disease.
What to do is completely different:
Suspected heart attack: call emergency services immediately. Keep the person still and calm. Do not drive them yourself if an ambulance is available.
Cardiac arrest: call emergency services, start chest compressions immediately, and send someone for a defibrillator. Compressions hard and fast in the centre of the chest keep blood moving; a defibrillator can restore a normal rhythm. Survival falls with every minute of delay, and bystander CPR roughly doubles or triples the chance of survival.
Defibrillators are designed for untrained users — they speak instructions and will not shock a heart that does not need it.
General information, not medical advice. In an emergency, call your local emergency number.