Lastly, to study the signaling pathways linking GCH1 with cardiac remodeling, we determined cardiac BH4 concentrations, free Ca2+ and SR Ca2+ release in cardiomyocytes in the presence and absence of isoproterenol, and the expression of microRNA-21, p38 MAPK, 3 isoforms of NOS, and SR Ca2+ handling proteins in Tg and C57BL/6 mice 4 weeks after MI or sham surgery. The gene discussed is GCH1; the disease is myocardial infarction.