The three kindreds studied included one in Iceland, one in the St. Lawrence region in Canada, and one in the Pittsburgh, Pennsylvania area. Pedigrees were established for the three kindreds. All family members were clinically evaluated by physical exam, electrocardiogram, and comprehensive M-mode and two-dimensional echocardiography. Lymphoblastoid cell lines were derived from all members of the three pedigrees. Restriction fragment length polymorphism analyses were used to identify a DNA probe that was linked to familial hypertrophic cardiomyopathy. Studies were conducted to determine if the familial hypertrophic cardiomyopathy locus was the same in all three kindreds and to identify the gene responsible.