A patient suffering from tsutsugamushi disease underwent endomyocardial biopsy for the purpose of diagnosis of myocarditis. Proliferation of Rickettsia tsutsugamushi was observed in the vascular endothelial cells of the myocardium. There have been no reports describing the identification of Rickettsia tsutsugamushi endomyocardial biopsy. This report indicates that endomyocardial biopsy may be a useful adjunct to the clarification of myocardial involvement of Rickettsia tsutsugamushi.