Eligible patients were interviewed and asked whether any first-degree relatives were willing to participate. If family members participated, a three generation pedigree was constructed and first-degree relatives contacted. The relatives were interviewed for a medical history and medical records from other institutions were reviewed. Each family member had a brief cardiovascular examination, a 12-lead electrocardiogram and 2-dimensional, M-mode, and Doppler echocardiogram. Blood was drawn for determination of atrial natriuretic peptide (ANP) levels. The contributions of variability in age, sex, drug use, smoking, and other concomitants to variability in ANP and echocardiographic data were estimated. After removing these sources of variability, the strength of similarity among family members was assessed. The relative contributions of genes and shared environments to the similarity among family members were estimated.