This article was last reviewed on
This article waslast modified on 29 October 2019.

A heart attack (also called a myocardial infarction or MI) is defined by evidence of heart damage, shown by release of cardiac biomarkers, in the presence of poor blood supply (ischaemia). This can occur when a clot forms in one of the heart's coronary arteries and blocks the blood supply to part of the heart muscle. The blood clot develops on a narrowing of the coronary artery caused by fat deposition called atherosclerosis or atheroma. The blockage destroys heart tissue and can be fatal if not treated within an hour or two. Any cause of blood reduction to the heart can cause a heart attack including artery spasm or major blood loss or an increase in demand for oxygen for example when the heart beats very fast in a tachyarrhythmia.

The acute coronary syndrome (ACS) is a group of symptoms and signs including sudden chest pain which often spreads to the jaw, arm or shoulder caused by insufficient blood flow to heart muscle. Anyone with ACS should be taken to hospital as an emergency to find out whether the cause is a heart attack, unstable angina or a problem outside the heart. The tests done in patients presenting to hospital with a suspected heart attack often include an electrocardiogram (ECG) and measurement of heart muscle proteins (cardiac biomarkers e.g. troponin) in blood.

There are more than 100 risk factors for atherosclerosis. The major ones are divided into non-modifiable e.g. male sex, family history of premature cardiovascular disease and age, and modifiable e.g. high cholesterol, diabetes, high blood pressure and smoking. Treatment of an atherosclerotic heart attack is to restore the heart muscle’s blood supply such as surgery called coronary angioplasty to widen the coronary artery.

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About Heart Attack
  • Symptoms and signs

    Symptoms of the acute coronary syndrome (ACS) may include:

    • A pressing or squeezing pain in the centre of the chest, sometimes spreading to the jaw, arm, back or abdomen
    • shortness of breath, sometimes coughing or wheezing
    • feeling sick and light headed
    • a great feeling of anxiety

    Signs may include a rapid pulse, low blood pressure, pallor of the skin and sweating.

    In some cases the pain is minor and can be mistaken for indigestion. Symptoms may occur without any chest pain, particularly in older individuals and in those with diabetes. In women symptoms are often less dramatic and more likely to be misinterpreted as due to another cause than in men.

    If you experience these symptoms, dial 999 immediately for an ambulance. Do not worry if you are uncertain whether you are having a heart attack. Between 60% and 80% of patients taken to hospital with chest pain are found not to have had a heart attack. Paramedics would rather be called out to a false alarm than arrive too late to save a life.

    If someone who complains of severe chest pain becomes unconscious and no pulse can be felt, it could be due to a cardiac arrest caused by a heart attack. Their life could be saved if cardiopulmonary resuscitation is commenced and performed until the paramedics arrive. Find out how here.

  • Tests

    When a person with the acute coronary syndrome (ACS) arrives as an emergency at hospital, a number of tests are done urgently to help decide whether the cause is a heart attack, unstable angina or a problem outside the heart.

    An electrocardiogram (ECG) is performed within the first few minutes. Those who have a major clot completely blocking a coronary artery and damaging a large area of heart muscle tissue show the most severe changes in the ECG tracing, with a part of the line called the ST segment elevated above the baseline. This is called an ST segment elevation myocardial infarction or STEMI. More commonly the block is only partial, less muscle is damaged and the ST segment is not elevated. This is called a non-STEMI or NSTEMI. Unstable angina is a less serious form of ACS. The blood supply to the heart muscle is severely restricted but there is usually no permanent damage.

    Patients with ACS who have no ST segment elevation need blood tests to find out whether they have a non-STEMI, unstable angina or a non-cardiac condition. When heart muscle cells die they release proteins (cardiac biomarkers) into the blood. Raised levels can detect a heart attack, provide an indication of how much muscle has been damaged and also give an indication of response to treatment. The most specific blood tests for heart muscle damage are cardiac troponins T and I (TnT and TnI). High sensitivity troponin tests can rapidly rule in and rule out heart damage.

    Other tests that may be done include a chest X-ray to exclude air between the lung and the lining of the chest wall (pneumothorax) and to look for fluid accumulation in the lungs (pulmonary oedema). Echocardiography can help identify the area of heart damage and its effect on heart function.

  • Treatment

    The two principal treatments for a myocardial infarction are thrombolysis and angioplasty. In thrombolysis a ‘clot-busting’ drug is injected that attacks and dissolves fibrin that forms the protein meshwork of the clot. Other blood-thinning drugs such as low dose aspirin or heparin may also be given to prevent the clot reforming. In angioplasty, a thin catheter is passed through an artery in the groin or arm to the narrowed coronary artery under X-ray guidance using a radio-opaque dye and a balloon at its tip inflated. Often a flexible wire mesh tube called a stent is implanted to hold the widened artery open.

    Patients with a STEMI usually have urgent angioplasty. However, if the patient cannot be taken to a UK Heart Attack Centre within two and a half hours, thrombolysis is used instead. Patients with a non-STEMI are usually treated with ‘clot-busting’ drugs initially, although angioplasty may be needed later. Patients with ACS due to angina often have angioplasty after further investigations. When angioplasty may be a problem because of extensive arterial narrowing, a coronary artery bypass graft (CABG) may be considered. A blood vessel from another part of the body is used as a graft to replace narrowed arteries in the heart.

    Recovery from a heart attack may take several months. Drugs may be prescribed to help heart function, control blood pressure and lower cholesterol. Advice will be provided about exercise during rehabilitation, and life style changes including adopting a prudent diet, maintaining a healthy weight and not smoking are recommended.