Viagra works by acting as a phosphodiesterase type 5 or PDE-5 inhibitor. What that means is Viagra suppresses or changes how the body reacts to phosphodiesterase type 5 (PDE-5). When that happens, and when there is sexual stimulation, the chemical nitric oxide causes the smooth muscles in the penis to relax. This in turn allows more blood to reach the vessels in the penis. If sexual stimulation does not occur, a man will not get an erection. For an interesting and comprehensive explanation of how Viagra works, in layman’s terms, click here.