What happens during a heart attack?

During a heart attack, blood flow to the heart muscle is blocked. This is most commonly due to coronary artery disease.

Discover how the heart works, how risk factors contribute to a heart attack and the importance of reducing your risk factors.

After having a heart attack treated in hospital, it's easy to think that the problem has been dealt with - the heart attack is over and done with. However, a heart attack is usually a symptom of an underlying heart health problem like coronary artery disease (CAD).

What is coronary artery disease?

Most heart attacks are caused by coronary artery disease (also called atherosclerosis). This is when a gradual build-up of fatty streaks (plaque) form in the coronary arteries. These are the arteries that deliver oxygenated blood to the heart muscle. The build-up of fatty streaks makes the coronary arteries narrow and stiffen over time.

As the coronary arteries narrow, it becomes more difficult for oxygenated blood to reach the heart muscle, sometimes causing pain and discomfort known as angina.

If a piece of plaque cracks, it may cause a blood clot to form and block a coronary artery, cutting off the blood supply to a part of the heart muscle. This causes a heart attack.

The heart attack symptoms you feel during a heart attack are caused by your heart muscle being starved of oxygen. This prevents your heart from beating as normal.

coronary artery disease angina heart attack comparison graphic

Causes of coronary artery disease

When you are young, your coronary arteries usually have smooth healthy walls. As you get older, the inner lining of your coronary arteries comes under attack from risk factors like toxins from cigarette smoke, mechanical injury from high blood pressure, high cholesterol or blood sugar from a diet high in saturated fats and sugars, and lack of exercise. These injuries start a chain of events that lead to the build-up of fatty streaks in your coronary arteries.


Other risk factors are within your power to change, such as smoking, high cholesterol, high blood sugar (diabetes), high blood pressure, being overweight, physical inactivity, poor nutrition and poor mental health and wellbeing.

There are choices you can make today to better manage your coronary artery disease and help to lower your risk of having another heart attack.

Can you have another heart attack?

After having a heart attack, you are at risk of having another one. Many people do not recognise their next heart attack, as it may feel different to the first one.

If you think you may be having a heart attack and you have already had one:

  • Stop and rest. Tell someone how you feel
  • If you take angina medication and the symptoms have not been relieved within 10 minutes, or if the symptoms are severe or getting worse,
  • Dial 111 and ask for an ambulance. If instructed and aspirin is available, take one.
Learn all the warning signs