Congenital heart disease represents a major segment of clinically significant birth defects and is associated with high mortality and morbidity in infancy, a childhood marred with physical limitations and repeated invasive procedures, and an adulthood with increased risk of medical and social problems. Previous research has been principally directed to clinical methods of diagnosis and treatment, but the need for prediction and prenatal counseling requires further knowledge of environmental and familial risk factors. Congenital heart disease is not one of the malformations monitored by the International Clearing House of Birth Defects Surveillance System. Surveillance which does include congenital heart disease may lack diagnostic accuracy among the various reporting sources. Accurate clinical studies lack comparative control information. As a result, the true epidemiologic features of cardiac defects remain obscure.