Hypoplastic left heart syndrome (HLHS) is a type of congenital heart disease that results in the underdevelopment of the left-sided structures of the heart, including the mitral valve, left ventricle, aortic valve, ascending aorta, and aortic arch. HLHS was first described as a syndrome in 1958 by Nadas and NoonanFontanwho referred to it as combined aortic and mitral atresia.[1] HLHS affects 1 in 5,000 neonates or 3% of all infants born with congenital heart disease.[2][3] Thirty years ago, there were no treatment options for these neonates, and mortality was 100% within the first week of life.[4] Neonates born with HLHS are dependent on a patent ductus arteriosus and an interatrial communication for survival until surgical intervention. A continuous infusion of prostaglandin E1 (PGE1) is needed to maintain ductal patency. Today, several treatment options are available in the prenatal or neonatal period, including the Norwood procedure, hybrid stage 1, heart transplantation, palliative care, and fetal intervention. A series of three palliative surgical operations (Norwood/Hybrid, Hemi-Fontan/Bidirectional Glenn, and Fontan) are typically necessary for survival beyond the neonatal period and infancy. Though rare, a diagnosis of HLHS is responsible for 23% of all cardiac deaths in the first week of life.[1
