Myocarditis is an inflammation of the myocardium, the middle layer of the heart wall. A variety of signs and symptoms, including chest pain, heart failure and abnormal heart rhythms, can be caused by myocarditis.

Garvan J. Lynch
MBA (Public Health)

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What is it?

Myocarditis is an inflammation of the myocardium, the middle layer of the heart wall. A variety of signs and symptoms, including chest pain, heart failure and abnormal heart rhythms, can be caused by myocarditis.

If myocarditis becomes severe, the pumping action of your heart weakens, and your heart won't be able to supply the rest of your body with enough blood. Clots also could form in your heart, leading to a stroke or heart attack.

Myocarditis is usually caused by a viral infection. Treatment for myocarditis depends on the underlying cause.


The signs and symptoms of myocarditis vary, depending on the cause and the severity of the disease. Common myocarditis symptoms include:

  • Chest pain
  • A rapid or abnormal heartbeat (arrhythmia)
  • Shortness of breath, at rest or during physical activity
  • Fluid retention with swelling of your legs, ankles and feet
  • Fatigue
  • Other signs and symptoms you'd have with a viral infection, such as a headache, body aches, joint pain, fever, a sore throat or diarrhoea

In mild cases, myocarditis may have no noticeable symptoms. You may feel ill and have general symptoms of a viral infection and never realize your heart is affected.

Myocarditis in children

When children develop myocarditis, they may experience these signs and symptoms:

  • Fever
  • Fainting
  • Breathing difficulties
  • Rapid breathing
  • Bluish or greyish discoloration of the skin 


Often, the exact cause of an individual case of myocarditis isn't identified. However, there are numerous potential causes of myocarditis, such as:

  • Viruses. Viruses commonly associated with myocarditis include coxsackievirus B, which can cause symptoms similar to a mild case of flu; the viruses that cause the common cold (adenovirus); and parvovirus B19, which causes a rash called fifth disease. Gastrointestinal infections (echoviruses), mononucleosis (Epstein-Barr virus) and measles (rubella) also are causes of myocarditis. Myocarditis is also common in people with HIV, the virus that causes AIDS.
  • Bacteria. Numerous bacteria may cause myocarditis, including staphylococcus, streptococcus, the bacteria that causes diphtheria and the tick-borne bacterium responsible for Lyme disease.
  • Parasites. Among these are such parasites as Trypanosoma cruzi and toxoplasma, including some that are transmitted by insects and can cause a condition called Chagas' disease. This disease is much more prevalent in Central and South America than in the United States, but it can occur in travelers and in immigrants from that part of the world.
  • Fungi. Some yeast infections (such as candida), moulds (such as aspergillus) and other fungi (such as histoplasma, often found in bird droppings) can sometimes cause myocarditis.

Myocarditis also sometimes occurs if you're exposed to:

  • Medications that may cause an allergic or toxic reaction. These include antibiotics, such as penicillin and sulfonamide drugs, some anti-seizure medications as well as some illegal substances, such as cocaine.
  • Other diseases. These include lupus, connective tissue disorders and rare inflammatory conditions, such as Wegener's granulomatosis.


When myocarditis is severe, it can permanently damage your heart muscle. This damage may cause:

  • Heart failure
  • Blood clots
  • Heart attack
  • Stroke
  • Irregular heartbeats (arrhythmias)
  • Sudden death

In very severe cases, myocarditis-related heart failure requires an artificial heart or heart transplant.


If your doctor suspects myocarditis, he or she may also order one or more tests in addition to asking you questions and examining you to make a diagnosis of myocarditis and determine the severity of your condition, including:

  • Electrocardiogram (ECG). This noninvasive test shows your heart's electrical patterns and can detect abnormal rhythms, as well as a weakened or damaged heart muscle.
  • Chest X-ray. An X-ray image of your chest allows your doctor to check the size and shape of your heart, as well as look for fluid in or around the heart that might indicate heart failure.
  • MRI. Cardiac magnetic resonance imaging (MRI) will show your heart, its size, shape and structure. This test can show signs of inflammation of the heart muscle and help make or confirm a diagnosis of myocarditis.
  • Echocardiogram. Sound waves, or ultrasound, can create moving images of the beating heart. An echocardiogram may detect enlargement of your heart, poor pumping function, valve problems or fluid around your heart.
  • Blood tests. These tests measure white and red blood cell counts, as well as levels of certain enzymes that indicate damage to your heart muscle. Blood tests can also detect antibodies against viruses and other organisms that may mean you have a myocarditis-related infection.
  • Cardiac catheterization and endomyocardial biopsy. In this test, a small tube (catheter) is inserted into a vein in your leg or neck, and then is threaded into your heart. A special instrument can remove a tiny sample of heart muscle tissue (biopsy) for analysis in the laboratory to see if there are signs of inflammation or infection.


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