While many conserved cardiogenic genes described at the beginning of this article play fundamental roles in heart development and are thus less likely to be directly involved in the etiology of HLHS, factors such as Islet1 (Isl1) and Notch1 can modulate the balance of different lineages of cardiac cells to control the size of cardiomyocyte population. The gene discussed is ISL1; the disease is hypoplastic left heart syndrome.