The Mef2c anterior heart field enhancer and promoter (AHF) was cloned into a cre expression plasmid with the cre cDNA and the SV40 splice sequence and the polyA signal sequence. The Mef2c-AHF-Cre fragment was injected into male pronuclei of fertilized oocytes. Three founder lines were initially characterized and line 200A was used for further analysis.