Editorial Comment Distinct Forms of Myocarditis

T he study by Davidoff and colleagues in this issue of Circulation' is helpful because it establishes clinically useful distinctions between two forms of myocarditis. In thinking about etiologies of myocarditis, I find it helpful to consider six categories. The first, viral myocarditis, is caused by ongoing myocardial infection, such as by coxsackievirus B3 or mumps virus. All other infectious causes form the second category. Chagas' disease (Trypanosoma cruzi), toxoplasmosis, and diphtheria are examples. Among these, only Chagas' myocarditis is common, and it might be the most common etiology of myocarditis throughout the world. The third category