Causes - Heart attack

Heart attacks are caused by the blood supply to the heart being suddenly interrupted. Without this supply, heart muscles may be damaged and begin to die.

Without treatment, the heart muscles will experience irreversible damage.

If a large part of the heart is damaged, the heart stops beating (known as a cardiac arrest), resulting in death.

Coronary heart disease

Coronary heart disease (CHD) is the leading cause of heart attacks. CHD is a condition where the coronary arteries get clogged up. They get blocked by deposits of cholesterol. Coronory arteries are the major blood vessels that supply the heart with blood. The deposits that clog up the arteries are called plaques.

Before a heart attack, one of the plaques bursts. This causes a blood clot to develop at the site of the rupture. The clot may block the supply of blood to the heart, triggering a heart attack.

Your risk of developing CHD is increased by:

  • smoking
  • a high-fat diet
  • diabetes
  • high cholesterol
  • high blood pressure
  • being overweight or obese

Less common causes of heart attacks

Drug misuse

Stimulants can cause coronary arteries to narrow.

This includes drugs like:

  • cocaine
  • speed
  • crystal meth

If the coronary arteries narrow, it restricts blood supply. This can trigger a heart attack.

Heart attacks from the use of cocaine are one of the most common causes of sudden death in young people.

Lack of oxygen in the blood (hypoxia)

Levels of oxygen in the blood may fall because of:

  • carbon monoxide poisoning
  • a loss of normal lung function

If this happens, the heart will receive unoxygenated blood.

This will damage the heart muscles, and this damage will trigger a heart attack.


Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 25 March 2021
Next review due: 25 March 2024

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