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Diagnosis - Heart attack

If a heart attack is suspected, you'll be taken into hospital immediately.

You will usually be admitted to a coronary care unit.

But you might go straight to the cardiac catheterisation unit. This is to confirm the diagnosis and begin treatment.


An electrocardiogram (ECG) is an important test in suspected heart attacks. You should have it within 10 minutes of arriving at hospital.

An ECG measures the electrical activity of your heart. Every time your heart beats, it produces tiny electrical impulses.

An ECG machine records these signals onto paper. This allows your doctor to see how well your heart is functioning.

An ECG is painless. It takes about 5 minutes to perform.

You will have electrodes (flat metal discs) attached to your arms, legs and chest.

Wires from the electrodes connect to the ECG machine. This records the electrical impulses.

An ECG is important because it helps to:

  • confirm the diagnosis of a heart attack
  • find out what type of heart attack you have had. This will help determine the most effective treatment

Types of heart attack

Heart attacks can be grouped by a measurement from the ECG known as the ST segment.

It corresponds to the area of damage inflicted on the heart.

Acute coronary syndrome

A heart attack is a form of acute coronary syndrome (ACS). This is where there is a significant blockage in the coronary arteries.

There are 3 main types of ACS:

  • ST segment elevation myocardial infarction (STEMI)
  • non-ST segment elevation myocardial infarction (NSTEMI)
  • unstable angina

ST segment elevation myocardial infarction (STEMI)

A STEMI is the most serious type of heart attack. It is where there is a long interruption to the blood supply.

This is caused by a total blockage of the coronary artery. It can cause extensive damage to a large area of the heart.

A STEMI is what most people think of when they hear the term "heart attack".

Non-ST segment elevation myocardial infarction (NSTEMI)

A NSTEMI can be less serious than a STEMI.

This is because the supply of blood to the heart may be only partially blocked.

As a result, a smaller section of the heart may be damaged. But a NSTEMI is still a serious medical emergency. Without treatment, it can progress to serious heart damage or STEMI.

Unstable angina

Unstable angina is the least serious type of ACS.

But it is still seen as a medical emergency. It can also progress to serious heart damage or STEMI.

In unstable angina, the blood supply to the heart is still limited. But there is no permanent damage so the heart muscle stays safe.

Other tests

Other tests can look at the state of your heart and check for related complications.

But, because heart attacks are emergencies, some tests usually only begin after you get treatment. They are done after you are in a stable condition.

Blood tests

Damage to your heart from a heart attack causes certain proteins to slowly leak into your blood. These special proteins are known as enzymes. They help regulate chemical reactions that take place in your body.

If you have had a suspected heart attack, a sample of your blood will be taken. This is so it can be tested for these heart proteins. These are known as cardiac markers.

The most common protein measurement is a cardiac troponin. Your troponin levels are measured through a series of blood samples taken over the course of a few days.

This will allow doctors to assess the damage to your heart. It will also help to determine how well you are responding to treatment.

Chest x-ray

A chest x-ray can be useful if diagnosis of a heart attack is uncertain.

There may be other possible causes of your symptoms. A pocket of air could be trapped between the layers of your lungs (pneumothorax).

A chest x-ray can also check whether complications have arisen from the heart attack. For example, a build-up of fluid inside your lungs (pulmonary oedema).


An echocardiogram is a type of scan that uses sound waves to build up a picture of the inside of your heart.

This can be useful to identify:

  • the areas of the heart that have been damaged
  • how this damage has affected your heart's function

Coronary angiography

Coronary angiography can tell if there is:

  • a blockage of the coronary arteries
  • narrowing of the coronary arteries

If so, this test can help to find the exact location of the blockage or narrowing.

The test involves inserting a thin tube, known as a catheter, into one of the blood vessels in your groin or arm. X-rays help guide the catheter into your coronary arteries.

A special fluid, known as a contrast agent, is pumped through the catheter. This fluid shows up on x-rays. Studying how it flows around and through your heart can help locate any blockage or narrowing. This helps your cardiologist decide the best treatment for you.

Complications from a heart attack

Potential complications from a heart attack can vary widely. They can range from mild to life-threatening.

Some people experience a "minor" heart attack with no associated complications. This is also known as an uncomplicated heart attack.

Other people experience a major heart attack, which has a wide range of potential complications. This may require extensive treatment.


An arrhythmia is an abnormal heartbeat – this includes:

  • beating too quickly (tachycardia)
  • beating too slowly (bradycardia)
  • beating irregularly (atrial fibrillation)

Arrhythmias can develop after a heart attack as a result of damage to the muscles. Damaged muscles disrupt electrical signals used by the body to control the heart.

Some arrhythmias, such as tachycardia, are mild and cause symptoms such as:

  • palpitations – the sensation of your heart racing in your chest or throat
  • chest pain
  • dizziness or lightheadedness
  • fatigue (tiredness)
  • shortness of breath

Other arrhythmias can be life-threatening. For example, a complete heart block or ventricular arrhythmia.

Complete heart block

Complete heart block is where electrical signals are unable to travel from one side of your heart to the other. This means your heart cannot pump blood properly.

Ventricular arrhythmia

This is where the heart begins beating faster before going into a spasm and stops pumping altogether. This is known as sudden cardiac arrest.

These life-threatening arrhythmias can be a major cause of death during the 24-48 hours after a heart attack.

However, survival rates have improved significantly since the invention of the portable defibrillator. This is an external device that delivers an electric shock to the heart and resets it to the right rhythm.

Mild arrhythmias can usually be controlled with medication such as beta-blockers.

More troublesome bradycardias that cause repeated and prolonged symptoms may need to be treated with a pacemaker. This is an electric device surgically implanted in the chest. It is used to help regulate the heartbeat.

Heart failure

Heart failure happens when your heart is unable to effectively pump blood around your body. It can develop after a heart attack if your heart muscle is extensively damaged. This usually occurs in the left side of the heart (the left ventricle).

Symptoms of heart failure include:

  • shortness of breath
  • fatigue
  • swelling in your arms and legs due to a build-up of fluid

Heart failure can be treated with a combination of medications and, in some cases, surgery.

Cardiogenic shock

Cardiogenic shock is similar to heart failure, but more serious. It develops when the heart muscle has been damaged so extensively it can no longer pump enough blood to maintain many of the body's functions.

Symptoms include:

  • mental confusion
  • cold hands and feet
  • decreased or no urine output
  • rapid heartbeat and breathing
  • pale skin
  • difficulty breathing

A type of medication called vasopressors (or inotropes) may be used. Vasopressors help constrict (squeeze) the blood vessels. This increases the blood pressure and improves blood circulation.

Once the initial symptoms of cardiogenic shock have been stabilised, surgery may be needed to improve the functioning of the heart. This may still include  percutaneous coronary intervention (PCI), alongside the insertion of a small pump, known as an intra-aortic balloon pump. This can help improve the flow of blood away from the heart.

Another option is a coronary artery bypass graft. This is where a blood vessel from another part of your body is used to bypass any blockage.

Heart rupture

A heart rupture is an extremely serious but relatively uncommon complication of heart attacks. This is where the heart's muscles, walls or valves rupture (split apart).

It can occur if the heart is significantly damaged during a heart attack. It usually happens 1 to 5 days afterwards.

Symptoms are the same as those of cardiogenic shock. Open heart surgery is usually required to repair the damage.

The outlook for people who have a heart rupture is not good. It's estimated that half of all people die within 5 days of the rupture occurring.

Aortic dissection

An aortic dissection is a serious condition in which the inner layer of the aorta tears. Blood surges through the tear. This causes the inner and middle layers of the aorta to separate (dissect).

An aortic dissection weakens the wall of the aorta, making it prone to rupture. A dissection may interrupt blood supply to any of the internal organs, arms or legs.

Aortic dissection is rare. It is a medical emergency and needs urgent treatment.

Aortic dissection is often fatal. But early diagnosis and treatment can greatly improve survival.

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

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

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