More reliable criteria for diagnosis of congenital heart disease were sought in a study of 128 subjects who submitted to cardiac catheterization. The data so obtained were found to be normal in 14 physicians who volunteered for catheterization and in 45 patients among the 114 suspected of having congenital heart disease. In 69 of the 114 the suspicion was confirmed. Analysis of these cases showed that clinical criteria can be depended on in the diagnosis of congenital heart disease in most adult patients with a persistent ductus arteriosus and left-to-right shunt as low as 40%, with an atrial or ventricular septal defect and left-to-right shunt as low as 25%, or a pulmonary valve stenosis and a systolic gradient as low as 40 mm. Hg.