Familial dilated cardiomyopathy (FDCM), an inherited primary form of myocardial disease, is a significant cause of morbidity and mortality at all ages and the leading reason for cardiac transplantation worldwide. Although typically inherited as an autosomal dominant disorder, all forms of inheritance have been recognized. FDCM appears to be responsible for approximately 20-30% of all cases of dilated cardiomyopathy, the most common form of cardiomyopathy. Recently, two families having autosomal dominant FDCM were mapped. The first family had conduction abnormalities and FDCM and was mapped to 1p1-1q1, while the second family, which had pure FDCM, was mapped to 9q13-q22. Neither gene has been identified to date. In this report, one family with pure FDCM was analyzed for linkage to the 1p1-1q1 and 9q13-q22 loci using parameteric linkage analysis, with linkage to both regions excluded. This demonstrates that the pure form of FDCM is caused by multiple different genes, i.e., genetic heterogeneity. Identification of large families with FDCM will be required to identify the various genes responsible for this important clinical entity.