Hypoplastic left heart syndrome is one of the most therapeutically challenging congenital cardiac defects. It accounts for as many as 1.5% of all congenital heart defects, but is responsible for up to one quarter of deaths in neonates with heart disease.1 The management of hypoplastic left heart syndrome is controversial. Two surgical options exist:2,3 the Norwood procedure, is a three stage repair in which the morphologically right ventricle is converted to function as the systemic ventricle. Alternatively, orthotopic transplantation can be performed. Although both surgical options have had improved outcomes, the prognosis for long-term survival is guarded, with a five year survival for either approach reported to be in the region of 50–60%. In this review, I explore the evidence for a genetic etiology for the “classic” hypoplastic left heart syndrome, defined as mitral and/or aortic atresia with hypoplasia of the left ventricular cavity and the other left-sided structures.