Inflammation of the heart muscle, usually in the U.S. as a consequence of infections (viruses, esp. coxsackie virus, and occasionally as a consequence of bacterial, protozoan or fungal infections); immunological-rheumatological conditions (e.g., systemic lupus erythematosus, ulcerative colitis, hypersensitivity reactions, or transplant rejection); exposure to chemicals or toxins (e.g., cocaine, doxorubicin, methamphetamine); nutritional or metabolic abnormalities (e.g., thiamine deficiency or hypophosphatemia); or radiation. Myocarditis also is occasionally found in pregnancy and with advanced age. The myocardium is infiltrated by leukocytyes, lymphocytes, and macrophages, leading to inflammation, necrosis of muscle cells, and fibrosis. Inflammatory damage to heart muscle fibers may resolve spontaneously or may cause progressive deterioration of the heart with pericarditis, arrhythmias, chronic dilated cardiomyopathy, and heart failure.
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