Clinical assessment of cases and controls included medical history, pedigree construction, complete evaluation by a pediatric cardiologist, and two-dimensional and Doppler echocardiography. First degree relatives of cases and controls underwent clinical-echocardiographic evaluation also. The distribution of cardiac defects for all pedigrees within and among the proband group was delineated. The frequencies of heart defects were compared within and among pedigrees of cases and controls. Regressive logistic models of genetic determinants for the malformations were tested. The three participating clinical centers included University of Maryland at Baltimore, the Johns Hopkins Hospital, and the University of Rochester in Rochester, New York.