Dilated cardiomyopathy (DCM) affects about 200,000 Canadians. Eighty percent of these cases are of unclear cause, often occuring in families. We believe that mutations in specific already-identified genes contribute to DCM in Quebec and that certain mutations may account for a significant proportion of cases due to the well-documented "founder effect". Two hundred patients with DCM followed in our Heart Function Clinic will be approached for one blood sample at their routine clinic visit to test this hypothesis. The samples will be tested in the Laboratory of Cardiovascular Genetics at the Royal Victoria Hospital.