Although the cause of HLHS is unknown, severe cardiomyopathy is thought to be a complex genetic disorder [7]; the genetic analysis of families with inherited left heart abnormalities (including HLHS, a bicuspid aortic valve, and coarctation of the aorta) have identified a few genes in which mutations are likely to be causative (notably NKX2.5 [8], NOTCH1 [9–11] and MYH6 [5, 12, 13]). This evidence concerns the gene NOTCH1 and hypoplastic left heart syndrome.