L-Arginine (2-amino-5-guanidino-pentanoic acid) is a conditionally essential, proteinogenic amino acid that is a natural constituent of dietary proteins. L-arginine is a precursor for nitric oxide (NO) synthesis. NO is a ubiquitous mediator that is formed by a family of enzymes named NO synthases. In the cardiovascular system, NO mediates the protective effects of the intact endothelium, acting as a vasodilator and endogenous antiatherogenic molecule.