Cardiac disease is the most common congenital defect in children, affecting between 3 and 10 in every 1000 live births. While significant advances in medical and surgical management have resulted in increasing numbers of survivors, it is also recognized that there is a growing population of children living with neurological impairment and lowered intellectual function. The aetiology of such impairment is multi-factorial and hypoxia is one of the factors involved. This article provides an overview of the effects of hypoxia on the intellectual development of infants, children and adolescents with congenital heart disease.