national referral centre		see supraregional referral centre (SRRC).
non-restrictive VSD		see ventricular septal defect.
Noonan syndrome		An autosomal dominant syndrome phenotypically somewhat similar to Turner syndrome, with a normal chromosomal complement, due to an abnormality in chromosome 12q. It is associated with congenital cardiac anomalies, especially dysplastic pulmonic valve stenosis, pulmonary artery stenosis, ASD, tetralogy of Fallot, or hypertrophic cardiomyopathy. Congenital lymphedema is a common associated anomaly that may be unrecognized. (Noonan JA, Ehmke DA. Associated non-cardiac malformations in children with congenital heart disease. Midwest Soc Pediatr Res 1963;63:468.)
Norwood procedure		A multistage operation for hypoplastic left heart syndrome. A systemic to pulmonary arterial shunt is created, followed by a staged Fontan-type operation (usually via a hemi-Fontan procedure) resulting in single ventricle physiology. The morphologic right ventricle supports the systemic circulation.