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 portion of the heart is damaged in this way, the heart stops beating (known as a cardiac arrest), resulting in death.

Coronary heart disease (CHD) is the leading cause of heart attacks. CHD is a condition in which the coronary arteries (the major blood vessels that supply the heart with blood) become clogged with deposits of fats such as cholesterol and other substances. These deposits are called plaques.

Before a heart attack, one of the plaques ruptures (bursts), causing a blood clot to form 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 (hypertension)
• being overweight or obese

Find out more about the causes of coronary heart disease (CHD).

A less common cause of heart attacks is a lack of oxygen (hypoxia).

If levels of oxygen in the blood decrease due to carbon monoxide poisoning or a loss of normal lung function, the heart will not receive enough oxygenated blood.

This will result in the heart muscles being damaged, triggering a heart attack.