Hypoplastic left heart syndrome

**Definition:** A spectrum of congenital cardiovascular malformations with normally aligned great arteries without a common atrioventricular junction, characterised by underdevelopment of the left heart with significant hypoplasia of the left ventricle including atresia, stenosis, or hypoplasia of the aortic or mitral valve, or both valves, and hypoplasia of the ascending aorta and aortic arch.