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Myocarditis – pronounced my-o-card-eye-tis – happens when the heart muscle (the myocardium) becomes inflamed and swollen.

Overall, this inflammation of the heart muscle and surrounding tissue is rare. It’s most often caused by a viral infection that makes its way to the heart. Influenza (flu), Coxsackie, Parvovirus (the cause of “fifth disease”), and viruses that cause the common cold are a few examples. 

Inflammation or swelling can occur when our immune system responds to fight an infection or heal an injury.

You may have heard more about myocarditis recently given concerns over whether the SARS-CoV-2 virus (the virus that causes COVID-19) or the vaccines used to prevent COVID-19 might trigger inflammation of the heart muscle in some people, especially young boys. While cases have been reported, they are still rare.

Myocarditis is more likely to occur from a COVID-19 infection than as a result of vaccination. There are several theories about how COVID-19 might cause myocarditis by either directly infecting the heart muscle or through other ways. Research is ongoing.

Other possible causes of myocarditis, include:

  • Bacterial infections, such as Chlamydia, Streptococcus aureus, Corynebacterium diphtheriae (causes diphtheria), Lyme disease (spread by ticks)
  • Fungal infections, such as yeast infections or thrush
  • Certain medications, including some chemotherapy drugs
  • Radiation therapy
  • Several autoimmune disorders in which the immune system attacks your body instead of protecting it; for example, lupus or myositis
  • Environmental exposures to toxins or heavy metals

Myocarditis can damage the heart muscle. It can also leave scar tissue in the heart, which can disrupt normal heart rhythms and cause symptoms of heart failure for some people.

Use this online resource to learn about myocarditis, how it’s treated, and questions to ask your health care team. 

  • Last Edited 12/08/2023