The myocardium is the muscular wall of the heart, or the heart muscle. It contracts to pump blood out of the heart and then relaxes as the heart refills with returning blood. The myocardium's smooth outer membrane is called the epicardium. Its inner lining is called the endocardium.

Myocarditis is an inflammation of the myocardium. When the heart becomes inflamed, it cannot pump as well because of damage to its cells and swelling (edema). The heart muscle may be damaged even more if your body's immune system sends antibodies to try to fight whatever started the inflammation. Sometimes, these antibodies attack the tissues of your heart instead. If too many heart muscle cells are damaged, the heart muscle becomes weakened. In some cases, this process happens very quickly and results in heart failure or even sudden death.

More often, the heart tries to heal itself by changing the damaged or dead heart muscle cells into scar tissue. Scar tissue is not like heart muscle tissue because it does not contract and it cannot help the heart to pump. If enough scar tissue forms in the heart, it can lead to congestive heart failure or dilated cardiomyopathy.

What causes myocarditis?

Myocarditis is a rare condition. The inflammation of the heart muscle may be caused by

• A viral, bacterial, or fungal infection.
• Rheumatic fever, which can occur if the antibodies that your body sends to fight a strep infection attack the tissues of your joints or heart instead.
• Drug or chemical poisoning.
• Connective tissue diseases, such as lupus or rheumatoid arthritis.

What are the symptoms?

With a mild case of myocarditis, you may not feel any symptoms at all. You may have a fever, an achy feeling in your chest, and severe fatigue, as if you have a bad cold or flu. Some people have an irregular heartbeat (arrhythmia) or trouble breathing. Usually, a mild case of myocarditis will go away without any lasting damage. Severe cases may not be diagnosed until you have the symptoms of heart failure. Even severe cases may go away without notice, but these severe cases usually cause ongoing and irreversible damage to the heart muscle.

How is myocarditis diagnosed?

Myocarditis is hard to diagnose because it can resemble many other diseases. Your doctor may suspect that you have myocarditis if your symptoms have appeared within 6 months of having an infection. A number of tests may be used to confirm the diagnosis:

• With a stethoscope, doctors can listen for a rapid heartbeat (called tachycardia).
   
• Blood tests to check for recent infection or signs of inflammation in the body.
   
• A chest x-ray can show doctors if there is a buildup of fluid in the lungs (called pulmonary edema). This is one of the signs of heart failure.
   
• Electrocardiography (an ECG or EKG) can help doctors learn more about your heart rhythm and the size and function of the chambers of your heart.
   
• Echocardiography can be used to see heart wall motion and overall heart size.
   
• A tiny sample of the heart muscle can be removed using a special device called a bioptome. This procedure is called an endomyocardial biopsy. The sample can then be tested for signs of infection.

How is myocarditis treated?

Myocarditis is treated with pain relievers and anti-inflammatory medicines. If myocarditis is part of another illness (such as rheumatoid arthritis), treating that illness will treat the heart as well. If myocarditis is caused by a bacterial infection, antibiotic medicines will be prescribed. In some cases, diuretics, digitalis, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, or vasodilators may be prescribed to help the heart pump while it heals. For patients who have arrhythmias, antiarrhythmic medicines may be prescribed. See Cardiovascular Medicines.

If myocarditis has not damaged the heart too much, medicines and follow-up visits to the doctor may be all that is needed. Other patients with more damage may need to limit some of their activities and take many medicines for the rest of their lives. For patients who have very severe damage to their heart, a heart transplant may be needed.

MedlinePlus
https://medlineplus.gov/ency/article/000149.htm
Myocarditis