To evaluate scar-type and matrix connective tissue and to assess their role in the diastolic dysfunction of hypertrophic cardiomyopathy, surgically resected subaortic myectomy specimens and several autopsy hearts from patients with hypertrophic cardiomyopathy were studied. Eighteen specimens were differentially stained by a newly developed method that precisely determines relative collagen content; these tissues were compared with postmortem hypertrophied and normal control subaortic specimens. Quantitation revealed a 72% higher level (36.5 vs. 22.1 micrograms collagen/mg protein) of stainable collagen in the hearts with hypertrophic cardiomyopathy than in hypertrophied control hearts. The endocardial plaque was quantitated morphometrically, and it constituted only 4.6 +/- 1.7% of the total increased collagen content in the cardiomyopathy specimens. For the matrix studies, the cardiomyopathy specimens were stained by a silver impregnation technique that identifies connective tissue elements not normally visible with routine histologic methods. There was a marked increase in content of all matrix components, both in areas of pathologic scarring and in "normal" zones. Whorls of matrix connective tissue were noted in regions of myocyte whorls, as well as independent of them. Thus, these studies revealed a striking increase of both scar-type and matrix connective tissue in hypertrophic cardiomyopathy. The extensive scarring and the pronounced interstitial and intercellular matrix connective tissue may contribute to the increased ventricular chamber stiffness and impaired relaxation in this disease.