Myocarditis is inflammation of the heart muscle.

The condition is called pediatric myocarditis when it occurs in children.

Inflammation - heart muscle

Myocarditis is an uncommon disorder. Most of the time, it is caused by an infection that reaches the heart.

When you have an infection, your immune system produces special cells to fight off disease. If the infection affects your heart, the disease-fighting cells enter the heart. However, the chemicals made by these cells can also damage the heart muscle. As a result, the heart can become thick, swollen, and weak.

Many cases are caused by a virus that reaches the heart. These can include the SARS-CoV-2 virus (the virus that causes COVID-19), influenza (flu) virus, coxsackievirus, parvovirus, cytomegalovirus, adenovirus, and others.

It may also be caused by bacterial infections such as Lyme disease, streptococcus, mycoplasma, and chlamydia.

Other causes of myocarditis include:

• Reactions to certain medicines, such as certain chemotherapy drugs
• Exposure to chemicals in the environment, such as heavy metals
• Infections due to fungus or parasites
• Radiation
• Autoimmune disorders that cause inflammation throughout the body
• Myocarditis following COVID-19 vaccination has been reported, but is very rare

Sometimes the exact cause may not be discovered.

There may be no symptoms. Symptoms may be similar to the flu. If symptoms occur, they may include:

• Chest pain that may resemble a heart attack
• Fatigue or listlessness
• Fever and other signs of infection including headache, muscle aches, sore throat, diarrhea, or rashes
• Joint pain or swelling
• Leg swelling
• Pale, cool hands and feet (a sign of poor circulation)
• Rapid breathing
• Rapid heart rate
• Shortness of breath

Other symptoms that may occur with this disease:

• Fainting, often related to irregular heart rhythms
• Low urine output

Treatment is aimed at the cause of the problem, and may involve:

• Antibiotics to fight bacterial infection
• Medicines called steroids to reduce swelling
• Intravenous immunoglobulin (IVIG), a medicine made of substances (called antibodies) that the body produces to fight infection, to control the inflammatory process
• Diuretics to remove excess water from the body
• Low-salt diet
• Reduced activity

If the heart muscle is weak, your provider will prescribe medicines to treat heart failure. Abnormal heart rhythms may require the use of other medicines. You may also need a device such as a pacemaker, or implantable cardioverter-defibrillator to correct a dangerous abnormal heartbeat. If a blood clot is in the heart chamber, you will also receive blood thinning medicine.

Rarely, a heart transplant may be needed if the heart muscle has become too weak to function.

The outcome can vary, depending on the cause of the problem and a person’s overall health. Some people may recover completely. Others may have lasting heart failure.

Complications may include:

• Cardiomyopathy
• Heart failure
• Heart rhythm problems
• Pericarditis

Contact your provider if you have symptoms of myocarditis, especially after a recent infection.

Seek medical help right away if:

• Your symptoms are severe.
• You have been diagnosed with myocarditis, and you have increased chest pain, swelling, or breathing problems.

Treat conditions that cause myocarditis promptly to reduce the risk.

Published Date: January 09, 2022
Published By: Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 08/24/2022.

Centers for Disease Control and Prevention. Safety of COVID-19 vaccines. www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/safety-of-vaccines.html. Updated August 22, 2022. Accessed August 24, 2022.

Cooper LT, Knowlton KU. Myocarditis. In: Libby P, Bonow RO, Mann DL, Tomaselli GF, Bhatt DL, Solomon SD, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12th ed. Philadelphia, PA: Elsevier; 2022:chap 55.

Knowlton KU, Anderson JL, Savoia MC, Oxman MN. Myocarditis and pericarditis. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 84.

McKenna WJ, Elliott PM. Diseases of the myocardium and endocardium. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 54.

Simon’s Heart is a nonprofit organization dedicated to raising awareness about, and preventing deaths from, conditions that cause sudden cardiac arrest in children.