Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect in which the entire left side of the heart (including the left ventricle, mitral valve, aortic valve, and ascending aorta) is severely underdeveloped and unable to support the systemic circulation. It is one of the most complex and life-threatening congenital heart conditions.
In a baby with HLHS, the single right ventricle must supply both the pulmonary and systemic circulations, which it can only do through connections that are normally present only in fetal life (the patent ductus arteriosus and the foramen ovale). When these connections begin to close after birth, circulation rapidly deteriorates. HLHS is fatal without intervention and typically presents within the first few days of life.
Treatment requires a series of three open heart operations performed at staged intervals: the Norwood procedure (first weeks of life), the Glenn operation (around 4 to 6 months), and the Fontan completion (around 2 to 5 years of age). These procedures reconstruct the circulation so that the single right ventricle becomes the main pumping chamber. Heart transplantation is an alternative considered in some cases.
Survivors of HLHS staged palliation require lifelong specialist follow-up in Adult Congenital Heart Disease (ACHD) services. Long-term risks include Fontan circulation failure, arrhythmia, liver disease from chronic venous congestion, and reduced exercise tolerance. The risk of sudden cardiac arrest is elevated compared to the general population, and some patients require ICD implantation.
« Back to Glossary Index