Light micrograph of a section of human heart tissue showing infectious myocarditis. This disease is the result of an immune response to a microbial infection of the heart, both the intramyocardial microvasculature and the large epicardial coronary arteries, which play an important role in the pathogenesis of infectious myocarditis. Further described, myocarditis is inflammation of the heart muscle (myocardium). This inflammation can reduce the heart?檚 ability to pump and cause rapid or abnormal heart rhythms. A viral infection is the usual cause of myocarditis and can be life-threatening if not treated in time