Causes and Complications of Myocarditis

What are the Causes and Complications of Myocarditis?

Myocarditis, also known as inflammatory cardiomyopathy, is an inflammation of the heart muscle. There are various causes but it is usually caused by a virus and can strike at any age.

What are the symptoms

The symptoms may include chest pain (often described as stabbing), shortness of breath, irregular heart beat and a decreased ability to exercise. Problems can last from hours to months and complications can include sudden cardiac arrest or heart failure due to dilated cardiomyopathy.

Symptoms in young children tend to be nonspecific, with poor appetite and general malaise, abdominal pain and chronic cough. Respiratory symptoms can be presented later in the illness with difficulty in breathing and consequently it is sometimes mistaken for asthma.

Many patients with myocarditis recover quickly and completely but it can be serious and death can result in some cases.

Viral infections which cause myocarditis

Your immune system can defeat many types of virus affecting many parts of your body. This means that many cases of viral myocarditis can go away unnoticed within a week or so.

However, myocarditis may typically develop at the same time as, or more often just after, a viral chest or throat infection. The most common infections causing myocarditis are viruses called adenovirus and Coxsackie B.

Other viruses which have been known to cause myocarditis include:

Sometimes the inflammation in the heart may last well after the virus has gone. This is because the immune system can over react and cause inflammation which persists for a time in the heart.

Idiopathic myocarditis - Myocarditis where the cause is unknown

Often the cause of myocarditis is never found (it's then called Idiopathic myocarditis). In the majority of these cases a virus is still likely to be the culprit – it's just that the specific virus could not be identified.

Non viral causes of myocarditis

As viruses account for the majority of myocarditis cases, other causes are relatively rare but they include:

  • Other infections. Various fungi, bacteria, parasites and other germs can infect the heart. For example:
  1. Lyme disease (Lyme borreliosis). This is an infection caused by a bacterium called Borrelia burgdorferi. The bacterium is carried by ticks and infected ticks are found throughout North America and Europe. You can catch this infection by being bitten by one of these ticks.
  2. Chagas disease (also known as American trypanosomiasis). This is an infection caused by a protozoan called Trypanosoma cruzi. Infections can be caught from bites by an insect called Triatominae or kissing bugs which are predominately found in Southern and Central America. With this infection the myocarditis develops many years after the initial infection and leads to the slow but progressive destruction of the heart tissue. This causes severe heart failure.
  3. Giant cell myocarditis. This is a very rare. It gets its name from abnormal cells which develop in the heart. The cause is unknown but it tends to develop in some people who have a thymoma - a growth on the thymus gland, systemic lupus erythematosus (SLE) - also known as lupus, or an overactive thyroid.
  4. Very occasionally some medicines can cause side affects which cause myocarditis.
  5. Myocarditis can arise following a heart transplant
  6. Miscellaneous causes. Myocarditis can for example, be caused by radiation, certain chemicals and poisons and even by excess alcohol.

What are the possible complications?

Complications will develop if the inflammation damages the fibres that conduct the electrical impulses in the heart or the heart muscle. These complications can advance quickly following sudden-onset (acute) symptoms. But some cases of myocarditis develop slowly, as with infection of Chagas' disease, and have no acute symptoms.

Possible complications include the sudden loss of consciousness (syncope), abnormally fast, slow or irregular heartbeats (cardiac arrhythmias) and heart failure which can present as shortness of breath, tiredness and swelling of the legs and ankles.


Treatment for myocarditis depends on its cause and severity. To avoid undue strain on the heart, bed rest is usually essential and physical exertion should be avoided for at least six months. Painkillers are usually prescribed to ease chest pain and lower a high temperature. No treatment will cure a viral infection.

Luckily for most patients with viral myocarditis, the virus clears away naturally within a week or so without treatment.

Steroids can be beneficial for giant cell myocarditis. Steroids have also been prescribed for other forms of myocarditis. However, there are no clinical studies which demonstrate them as being beneficial.

For the more uncommon causes of myocarditis, or if complications develop, a range of treatments may be appropriate. For example:

  • Drugs to treat irregular heartbeat or heart failure.
  • Antibiotic medicines if the myocarditis is caused by a bacterial infection.
  • Steroid medication if the cause is giant cell myocarditis.
  • Stop drinking alcohol if alcohol is the cause.
  • A pacemaker if irregular heart rhythms develop.

The prognosis?

Normally with viral myocarditis, the illness goes away by itself with symptoms lasting only a few days or weeks. However, some viral infections are more serious and can cause severe or persistent inflammation and resultant complications.

Complications are more likely with the more uncommon causes of myocarditis. Sometimes the inflammation does clear but the heart is left with elements of permanent damage. Patients may then be left with a level of heart failure which requires long-term medication. Occasionally, the inflammation and damage is so severe that the only option is a heart transplant.

Inevitably in some cases myocarditis is fatal. Death can occur some time after the diagnosis if the condition worsens or becomes unresponsive to treatment. With acute myocarditis sudden death can happen even where the patient was previously healthy.

Last Reviewed:
March 15, 2017
Last Updated:
September 26, 2017
Content Source:
  • Eckhardt G. J. Olsen. (1985.) “What is myocarditis?
  • Kenneth L. Baughman, Special Report: Diagnosis of Myocarditis 2006
  • Feldman AM, McNamara D (November 2000). "Myocarditis"