5'-AMP-activated protein kinase is considered as a "fuel gauge'' in the cell and is activated by an increase in AMP/ATP ratio. Upon activation AMP-kinase switches on ATP producing catabolic pathways such as fatty acid oxidation and switches off ATP consuming anabolic pathways like lipogenesis or gluconeogenesis. Physiological stress conditions which stimulate AMP-kinase are exercise, nutritional starvation, heat shock, oxidative stress, ischemia or hypoxia. Adult heart receives 60–90% of the energy by fatty acid oxidation, but the major energy source of energy for embryonic heart is glucose. In the present study the effect of AMPK on cardiovascular differentiation of mouse embryonic stem (ES) cells was investigated. The AMP- kinase activators AICAr and metformin increased NO production within one hour of treatment in a dose dependent manner and increased HIF-1a protein expression after 24h. Cardiac differentiation was increased by 50% in embryoid bodies treated with AMPK activators, and cardiac transcription factors as well as cardiac marker genes were upregulated. FACS measurement for cardiomyocytes and endothelial cells showed an increase in the number of both cardiac and endothelial cells. These experiments provide evidence for the role of AMPK cardiovascular differentiation of ES cells.