Energy pathways in cardiomyocytes. Multiple metabolic pathways provide adequate energy sources for cardiac requirements: Glycolysis, anaerobic metabolism, fatty acid metabolism, and the creatine energy buffer system (compartmentalization not shown). MR-visible metabolites are shown in bold font and include lactate, alanine, succinate, glutamate, glutamine, carnitine, and creatine. MDMA-induced changes in metabolite levels are shown in parentheses: ↑ = significant increase and ↔ = no change.