Transgenic mice in which Cre recombinase expression is driven by the Mef2c AHF enhancer have been used to determine anterior heart field derived structures and conditionally knock-out many developmental genes (Mef2c, Tbx1, β-catenin, Ezh2) to reveal their specific roles in anterior heart field development and congenital heart disease (Verzi et al., 2005; Delgado-Olguín et al., 2012; Barnes et al., 2016; Racedo et al., 2017). The gene discussed is MEF2C; the disease is congenital heart disease.