All cases involved white women, ages 19 to 25, with no previous medical history; weight of all hearts was normal; microscopic evidence of fibrosis was present in four cases; and there was evidence of scarring or interstitial fibrosis in all the cases. In four cases, inflammatory foci consisting of lymphocytes, plasmocytes, and macrophages were observed; and two cases demonstrated eosinophil and neutrophil aggregates in the center of necrotic foci. The evidence from these cases suggests that extensive sampling of inflammatory foci is required, inflammatory foci may be associated with myocardial fibrosis, and fibrosis may be the only evidence of a previous inflammatory process. The fibrosis indicates a predisposition to electric instability, reentry circuits, and fatal arrythmias. 3 figures and 8 references