This article summarizes the case histories of six infants who had isolated secundum-type atrial septal defects (ASDs) and presented with failure to thrive in the first year of life. Patients underwent operative closure of their ASD with the expectation that this would improve their feeding and growth pattern. Five of the six children demonstrated little or no improvement in symptoms following operation. Each of these five patients have subsequently shown signs of developmental delay. Our experience with this group suggests that failure to thrive associated with a secundum ASD will frequently have a noncardiac basis.