**2. Epidemiology and prognosis**

The clinical course of myocarditis varies. The symptoms range widely, from slight to severe, and it is difficult to investigate myocarditis epidemiologically. In 2002 in Japan, a large-scale investigation for cardiomyopathy was performed and reported that cardiomyopathy was found in 21.3 per 100,000 population (Miura et al., 2002). However, the subjects of this investigation were consulted patients with data provided by hospitals. It is thought that actual morbidity is higher, because there are many non-consulted persons with occult cardiomyopathy, such as early stage dilated cardiomyopathy or hypertrophic cardiomyopathy with no symptoms. Therefore, we still cannot grasp the exact morbidity of myocarditis in Japan. Okada et al. (1989) reported that among 10,000 autopsied cases during 1958–1978 there were 115 cases of myocarditis. In another report, occult myocarditis was found in 0.6% of autopsied cases in which cardiac disease had not detected while the patients were alive (Feely et al., 2000). Therefore, it should be recognized that myocarditis is not clinically infrequent and includes a mild type that displays no symptoms. The mortality rate for myocarditis has not been established. An investigative committee of the Ministry of Public Welfare and Labor in Japan reported in 1986 that 13 (4.7%) of 274 patients died within 1 month in a small-scale investigation targeting acute-phase myocarditis (Kawamura et al., 1986). Among those cases, the causes of death were cardiogenic shock in six cases (46%), congestive heart failure in five cases (38%), and complete atrioventricular block in two cases (15%). Intensive treatment for severe cardiac dysfunction and fatal arrhythmias are important to reduce mortality during the acute phase of severe myocarditis.
