Myocarditis is an uncommon inflammation of the heart muscle (myocardium). This inflammation can be caused by infectious agents, toxins, drugs or for unknown reasons. It may be localized to one area of the heart, or it may affect the entire heart.

Because the disease is so variable, it is difficult to diagnose and detect. If the myocarditis is caused by a virus (the most common cause in the industrialized world), the symptoms of the myocarditis may be masked by the viral infection. In some cases, patients may not be aware they are suffering from myocarditis at all. Among these patients, the myocarditis will likely resolve with no adverse effects. More serious cases of myocarditis, known as acute or fulminant, may require more aggressive treatment, even including a heart transplant. Fortunately, however, most patients with acute or fulminant myocarditis recover with time and treatment.

One complication of myocarditis is the presence of potentially deadly arrhythmias, or abnormal heart rhythms. To help identify and treat abnormal heart arrhythmias as soon as possible, patients with acute myocarditis may be monitored frequently and treated with special antiarrhythmic medications.

In an unknown number of patients, myocarditis can progress to dilated cardiomyopathy and heart failure. In these conditions, the heart expands as it tries to compensate for its weakened condition. As a result, it no longer pumps efficiently and there is a reduction in the flow of oxygen-rich blood to the body. Patients with heart failure caused by myocarditis are treated with standard measures for heart failure, including medications and devices designed to increase the pumping action of the heart.