Myocarditis is an inflammation of the heart tissue, specifically the myocardium, the middle layer of the heart wall. Myocarditis affects your heart’s electrical system and muscle cells, leading to irregular heart rhythms and problems with your heart’s pumping function. In severe cases, your heart becomes too weak to adequately pump enough blood to the rest of your body. You’re also more susceptible to clots forming in your heart, which could lead to a stroke or heart attack.