Eight patients with chronic myocarditis (CM), 2 showing postmyocarditis and 6 showing dilated heart with severe diffuse cell infiltration, were compared morphometrically with 27 patients with dilated cardiomyopathy (DCM, 8 with fibrosis type DCM and 19 with non-fibrosis type DCM) and 10 controls. Patients with CM had a mean age of 43.5 years (range, 17-75 years), a mean duration of clinical illness of 45.5 months, heart weight of 448 g, left ventricular wall thickness of 8 mm, number of myocyte layers of the stratum compactum layer of the left ventricle (Nf) of 125, myocyte size of 19.1 micron, and % area of fibrosis of 29.1%. The morphometric profile of patients with CM resembled that of patients with fibrosis type DCM; this appeared to be due primarily to a decrease in the number of myocardial cells and an increase in myocardial fibrosis.