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Myocarditis is inflammation of the heart muscle. Find out what causes myocarditis and how it's diagnosed and treated.

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What is myocarditis?

Myocarditis is inflammation of the heart muscle (myocardium). It can affect the whole heart muscle or just parts of it.

The inflammation can make the heart larger and weaker, which means the heart can't pump blood as well as it should. Most people with myocarditis recover without any complications. But, in rare cases, when inflammation is severe, there can be damage to the heart.

A diagram illustrating a healthy heart and a heart with myocarditis

What causes myocarditis?

A viral infection is the most common cause of myocarditis. This can include viruses such as the common cold (adenovirus), Hepatitis B and C, and Covid-19.

Bacterial and fungal infections can also cause it.

You can develop myocarditis if you have an autoimmune disease, for example, type 1 diabetes or rheumatoid arthritis. This is because the autoimmune disease can cause inflammation in other body areas.

Some medicines and illegal drug use can also cause myocarditis.

Can I get myocarditis from having the Covid-19 vaccine?

Myocarditis is a rare side effect of some Covid-19 vaccinations (including the Pfizer vaccination, also called Comirnaty). However, you're at greater risk of developing myocarditis due to catching the Covid-19 virus than you are from having the vaccine. The benefits of having the vaccine to protect against Covid-19 greatly outweigh the risks.

The risk of myocarditis is much greater from Covid-19 complications than vaccination.

Myocarditis symptoms

Symptoms of myocarditis include some or all of the following:

  • chest pain
  • a feeling of heaviness in the chest
  • difficulty breathing some or all of the time
  • a fast heartbeat/heart palpitations (a feeling like your heart is jumping around or skipping a beat)
  • tiredness
  • unable to carry out your usual daily activities
  • swelling in your legs and or feet.

Symptoms of myocarditis usually develop one to two weeks after a viral infection. After a Covid-19 vaccination, if symptoms were to appear it’s typically within a week, most often within the first five days.

How is myocarditis diagnosed?

If your doctor suspects myocarditis, you're likely to have some or all of the following tests:

  • an electrocardiograph (ECG) to check your heart rate and rhythm
  • blood tests to check for heart muscle damage and inflammation
  • chest x-ray to look at heart size and for fluid
  • echocardiogram to look at the structure of your heart.

Learn more about heart tests

How is myocarditis treated?

Treatment will vary for each person and depends on your symptoms.

If you have mild myocarditis, you may need to stay home, rest, and take medication.

If you have severe myocarditis, this will most likely require a stay in hospital.

You will have to keep your activity level low. Some people may need oxygen to help them with their breathing.

You may need medication to help:

  • prevent blood clots
  • keep your heart pumping normally and reduce the amount of work it's doing 
  • reduce excess fluid
  • help you with your breathing
  • reduce inflammation.

It is very important not to drink alcohol while you have myocarditis. This is because it can cause more damage to your heart.

Learn more about heart medications

What is the recovery time for myocarditis?

The recovery time from myocarditis will be different for everyone. Sometimes it can take several months.

Some people may get myocarditis more than once.

What is myopericarditis?

Some people can be diagnosed with myopericarditis, a combination of inflammation of the heart muscle (myocardium) and the pericardium (sac around the heart). It is mainly caused by a viral infection.

It is usually treated with anti-inflammatory medication, resting and avoiding physical activity for six months.

Recovery time can be three to six months.