In addition to confirming the increased expression of MYH7 in HLHS tissues containing MYH6 variants (Fig. 4, A and B), the findings in Fig. 5, D and E, that increased MYH7 expression is phenocopied in cardiomyocytes from iPSCs in two separate families, indicate that HLHS etiology can be investigated at the earliest stages of cardiomyogenesis using this in vitro disease model. This evidence concerns the gene MYH7 and hypoplastic left heart syndrome.