Nitric oxide is synthesized from an essential amino acid L-arginine in vascular endothelial cells, vascular smooth muscle cells, and cardiac tissues. Nitric oxide induces vasorelaxation, anti-growth effects, and negative inotropic effects. Therefore, nitric oxide is regarded as an important regulator for the cardiovascular system including atherosclerosis. This brief article reviews new information on nitric oxide, and discusses the clinical implications of nitric oxide for cardiovascular disease.