In The Lancet, Andrew Ewer and colleagues report their experience with pulse oximetry as a complementary method for detection of congenital heart disease in asymptomatic newborn babies. The study was commissioned by the National Institute of Health Research to assess whether pulse oximetry ought to be incorporated into the routine care of newborn babies. To answer this question, the team constructed a screening protocol for measurement of upper and lower limb oxygen saturations, and repeated screens to reduce false-positive rates.