The naturally occuring chemical nitric oxide not to be confused with nitrous oxide aka laughing gas is produced by endotthelial tisue that lines the blodd vessels… Look how much the interior of the beet root looks like the interior of veins or arteries… It helps widen the vessels and tiny capillaries, thus improbing the flow of blood. Viagra utilises thei role of nitric oide to imporve blood flo to the male sexual region.  The amino acid arginine helps its production and is found in nuts and animal products. Nitrate -rich beg such as beetroot, spinach and radish aslo boost its production.