The aim of this study was to assess the utility of arm and leg oxygen saturation as a candidate screening test for the early detection of ductal-dependent left heart obstructive disease. We measured arm and leg oxygen saturation in 2876 newborns admitted to well baby nurseries and 32 newborns with congenital heart disease. Fifty-seven newborns in the well baby nurseries (0.02%) had an abnormal test (leg saturation less than 92% in room air or 7% lower saturation in the leg than in the arm). Four of the 57 had critical congenital heart disease, including 1 with coarctation of the aorta. Of the 32 newborns with congenital heart disease, 11/13 (85%) with left heart obstructive disease had abnormal oxygen saturation tests, as did 15/19 (79%) with other forms of congenital heart disease. Pulse oximetry deserves further study as a screening test for critical congenital heart disease.