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In medicine (cardiology), myocarditis is inflammation of heart muscle (myocardium). It resembles a...

In medicine (cardiology), myocarditis is inflammation of heart muscle (myocardium). It resembles a heart attack but coronary arteries are not blocked. Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi (Lyme disease) or Trypanosoma cruzi, or as a hypersensitivity response to drugs. The definition of myocarditis varies, but the central feature is an infection of the heart, with an inflammatory infiltrate, and damage to the heart muscle, without the blockage of coronary arteries that define a heart attack (myocardial infarction) or other common non-infectious causes. Myocarditis may or may not include death (necrosis) of heart tissue. It may include dilated cardiomyopathy. Myocarditis is often an autoimmune reaction. Streptococcal M protein and coxsackievirus B have regions (epitopes) that are immunologically similar to cardiac myosin. After the virus is gone, the immune system may attack cardiac myosin. Because a definitive diagnosis requires a heart biopsy, which doctors are reluctant to do because they are invasive, statistics on the incidence of myocarditis vary widely. The