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Acute coronary syndrome

The underlying problem is a sudden reduction of blood flow to part of the heart muscle. This is usually caused by a blood clot.

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What is acute coronary syndrome?

The term 'acute coronary syndrome' (ACS) covers a range of disorders, including a heart attack (myocardial infarction) and unstable angina, that are caused by the same underlying problem. Unstable angina occurs when the blood clot causes a reduced blood flow but not a total blockage. This means that the heart muscle supplied by the affected artery does not die (infarct).

The underlying problem is a sudden reduction of blood flow to part of the heart muscle. This is usually caused by a blood clot that forms on a patch of atheroma within a coronary artery (which is described below).

The types of problems range from unstable angina to an actual myocardial infarction. In unstable angina a blood clot causes reduced blood flow but not a total blockage. Therefore, the heart muscle supplied by the affected artery does not die (infarct). The location of the blockage, the length of time that blood flow is blocked and the amount of damage that occurs determine the type of ACS.


  • The most common symptom is severe chest pain:

    • The pain often feels like a heavy pressure on your chest.

    • The pain may also travel up into your jaw and down your left arm, or down both arms.

    • It may be similar to a bout of normal (stable) angina. However, it is usually more severe and lasts longer. ACS pain usually lasts more than 15 minutes.

  • Some people with an ACS may not have any chest pain, particularly those who are elderly or those who have diabetes.

  • You may also sweat, feel sick and feel faint.

  • You may also feel short of breath.

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Risk factors

ACS is common. Most occur in people aged over 50 and become more common with increasing age. Sometimes younger people are affected.

The risk factors for having an ACS are actually the same as the risk factors for having a heart attack or cardiovascular disease. See the separate leaflet called Cardiovascular Disease (Atheroma) for more details.

What tests are usually done?

It can sometimes be difficult for doctors to distinguish between ACS and other causes of pains in the chest. If you are suspected of having ACS then you should be referred urgently to hospital. On admission to hospital, various tests are usually done. These are usually the same as for a suspected heart attack. One of the tests will be a heart tracing (electrocardiogram, or ECG). If you are having a heart attack, the ECG will help decide whether it is an ST-segment elevation myocardial infarction (STEMI) or a non-ST-segment elevation myocardial infarction (NSTEMI).

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The treatment of ACS varies between cases. A heart attack is treated differently to unstable angina. Treatments may vary depending on your situation. A STEMI usually causes more damage to heart muscle than an NSTEMI.

See the separate leaflet called Heart Attack (Myocardial Infarction) for more details of treatment for a STEMI.

Treatment of people with unstable angina or NSTEMI consists of two phases:

  • Relief of any pain.

  • Preventing progression to, or limiting the extent of, a heart attack.

Your treatment usually varies depending on your risk score. This is a risk score for a further heart attack. Various factors are taken into account for this score, including:

  • Your age.

  • Your other risk factors for cardiovascular disease (for example, if you smoke, have raised cholesterol or have high blood pressure or diabetes).

  • Your blood test results.

  • What your ECG looks like when you first attend the hospital.

See the separate leaflets called Heart Attack (Myocardial Infarction) and also Heart Attack Recovery for more details.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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