Nitric oxide (NO) is a Short-lived free radical produced endogenously in bilolgical tissues by nitric oxide synthases (NOSs)[1,2].Three NOS isoforms,namely NOSl or neuronal NOS (nNoS),NoS2 or inducible NOS(iNOS),and NoS3 or endothelial NOS(eNOS) are present in most cell types,including cardiac myocytes and vascular endothelial cells.Vascular relaxation to mediators such as acetvlcholine or increased blood flow depends on N0 produced by the eN0S.The discovery of NO as the endothelium-derived relaxing factor(EDRF) and its crucial function as a signaling molecule in cardiovascular system was awarded the Nobel Prize in Physiology or Medicine in 1998[1].