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Last Updated: Mar 1, 2019


Usually a viral infection like a cold or the flu is not cause for alarm (though we should always take the flu seriously). But in rare cases, these viruses can cause a potentially dangerous heart condition called myocarditis.

The heart is a muscular organ that pumps blood through a system of vessels to almost every cell in the body. This process, called circulation, supplies the cells with oxygen and carries off waste products. The heart is divided into four hollow chambers that contract to squeeze blood through the vessels.

Myocarditis is the inflammation (swelling) of the middle layer of the heart’s muscular wall, also known as the myocardium. The condition causes the heart to enlarge and thicken, weakening the chambers inside and reducing the heart’s ability to pump blood.

Mild myocarditis usually isn’t dangerous. However, more serious cases may lead to:

  • Clot formation. Blood pools in the weakened heart, forming solid masses. These clots can clog arteries in the heart or brain, causing a stroke or heart attack.
  • Arrhythmia. A fast or irregular heartbeat.
  • Heart failure. Due to poor circulation, the body’s cells don’t get enough oxygen and waste products build up.
  • Sudden death due to cardiac arrest. Experts believe that 5 to 20 percent of sudden deaths among young adults are related to myocarditis.

In a few cases, myocarditis can cause permanent damage to the heart, requiring lifelong medical care. In fact, about 45 percent of heart transplants in the United States are performed on people with myocarditis and a related disorder called idiopathic dilated cardiomyopathy.

Fortunately, myocarditis is pretty rare, with only a few thousands cases diagnosed each year in the United States. While exact numbers aren’t clear, it’s believed to occur during 1 to 5 percent of viral infections. Most of these cases are mild, have no heart-related symptoms, and are never diagnosed by a doctor.

Unlike other types of heart disease, myocarditis often strikes younger people with otherwise healthy hearts. Groups at increased risk include children (especially newborns), pregnant women and people with HIV infection.


Myocarditis develops when a pathogen (germ) infects the myocardium. The germ travels to the heart through the blood vessels, enters the myocardium cells and reproduces there. The body then sends special immune cells to fight the disease. Sometimes this immune response is so strong that it damages the heart along with the germ.

Viruses (including some very common ones) are the most common cause of myocarditis:

  • Coxsackievirus B (flu-like symptoms)
  • Adenovirus (common cold)
  • Parvovirus B19 (fifth disease)
  • Echoviruses (stomach flu)
  • Epstein-Barr virus (mononucleosis)
  • Rubella (German measles)
  • HIV.

Less common causes include:

  • Bacterial infections (notably Lyme disease)
  • Parasites
  • Fungal infections
  • Allergic reaction to drugs
  • Environmental toxins (for example, a venomous spider bite)
  • Autoimmune diseases that cause the immune system to attack healthy cells.


People with mild myocarditis often don’t have any heart-specific symptoms. However, they usually notice signs of an underlying infection, including body aches, joint pain, fever, sore throat, upset stomach, and diarrhea.

Heart-specific symptoms usually appear one to two weeks after the start of the underlying illness. The first is often shortness of breath during physical activity. This typically worsens and may eventually occur at rest or interfere with sleep.

Other common symptoms:

  • Chest pain or pressure
  • Lightheadedness
  • Arrhythmia (fast or irregular heartbeat)
  • Swelling due to fluid retention in the feet and lower legs
  • Feeling tired
  • Sudden loss of consciousness.

Myocarditis may look slightly different in babies and young children. Common pediatric symptoms include:

  • Rapid or labored breathing (can interfere with feeding in babies)
  • Skin that looks bluish or grayish
  • Cold, pale hands and feet
  • Urinating less or less frequently
  • Swelling of the face.


Anyone experiencing shortness of breath, chest pain or arrhythmia should seek medical attention. People with very mild symptoms can sometimes wait for a doctor’s appointment, but those with more serious symptoms should go to the nearest emergency department.

Myocarditis is diagnosed based on:

  • History and physical exam. Be sure to tell your doctor if you have had flu-like symptoms in the past few weeks.
  • EKG. An EKG is a test that measures the heart’s rhythm and electrical activity through the skin. Heart rhythms can also be monitored over time by a wearable device called a Holter monitor.
  • Chest x-ray. This imaging test can detect enlargement of the heart, lungs and blood vessels.
  • Echocardiogram. This imaging test uses high-pitched sound waves to show the heart and blood flow in motion. It’s especially useful for detecting blood clots.
  • Blood tests. When the heart muscle is damaged, blood levels of certain cardiac enzymes increase. Blood tests can also detect underlying infections that cause myocarditis.
  • Catheterization and endomyocardial biopsy. This procedure is the only way to diagnose myocarditis with certainty, but it is only used in severe cases. The doctor makes an incision in a large vein of the leg or neck and threads a catheter (flexible tube) toward the heart. An instrument is threaded through the tube and used to remove a small sample of heart tissue, which is then tested for signs of infection and inflammation.


The treatment of myocarditis depends on the underlying cause. Goals of care include:

  • Fighting the underlying infection
  • Restoring healthy circulation and heart rhythm
  • Relieving symptoms
  • Minimizing long-term damage to the heart.

People with mild myocarditis can often recover at home. Patients with arrhythmia or heart failure may need to stay in the hospital or even intensive care.

Many medications can help to manage myocarditis. In severe cases, they’re often given intravenously.

  • Anticoagulants prevent blood clots that can lead to heart attack and stroke.
  • Antimicrobials kill some types of bacteria and viruses that infect the heart.
  • ARBs and ACE inhibitors help relax and open the blood vessels so blood flows more easily.
  • Beta blockers normalize heart rhythm and combat some effects of heart failure.
  • Diuretics help to remove waste products that accumulate in cells during to heart failure.
  • Intravenous immunoglobulin - purified antibodies (proteins produced by the immune system) that reduce damage to the heart in some patients.
  • Steroids reduce inflammation caused by autoimmune disease.

Severe myocarditis cases might require:

  • Medical devices. Ventricular assist devices and intra-aortic balloon pumps are inserted into the heart to strengthen its pumping action.
  • Extracorporeal membrane oxygenation (ECMO). The patient is connected to a machine that draws the blood supply through a special membrane, removing carbon dioxide and adding oxygen. ECMO essentially acts as an external heart and lungs, allowing these organs to rest and heal.
  • Heart transplant. This is sometimes the best option when there has been severe, irreversible damage to the heart.

People recovering from myocarditis should rest and avoid exertion while the heart muscle heals. Heart failure patients may also benefit from a low-salt diet and fluid restrictions.


With proper treatment, about two-thirds of people with myocarditis recover completely. The remaining third experience long-term problems with arrhythmia and heart failure that require ongoing medication and management.

About 10 to 15 percent of myocarditis patients later have a recurrence. This can lead to cardiomyopathy, or chronic swelling of the heart. The symptoms and treatment of cardiomyopathy are similar to those of myocarditis.


The best thing you can do to prevent myocarditis is to avoid infections known to cause the condition:

  • Take normal precautions against germs, such as properly washing your hands and avoiding sick people.
  • Practice safe sex.
  • In tick-prone areas, wear protective clothing and insect repellant.
  • Get all recommended vaccines.


  • Discover Myocarditis Causes, Symptoms, Diagnosis and Treatment (2015). Myocarditis Foundation. Retrieved Oct. 27, 2015, from
  • Diseases and Conditions: Myocarditis (2015). Mayo Foundation for Medical Education and Research. Retrieved Oct. 27, 2015, from
  • Myocarditis (2014). Medscape. Retrieved Oct. 28, 2015, from
  • Pediatric myocarditis (2013). Cincinnati Children’s Hospital Medical Center. Retrieved Oct. 28, 2015, from

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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.