Viagra is the trade name of sildenafil citrate, a synthetic heterocyclic piperazine derivative marketed by Pfizer, Incorporated. Within the body, the drug acts by selective inhibition of cyclic guanosine monophosphate (cGMP) phosphodiesterase type 5, which facilitates the relaxation of smooth muscles and an influx of blood to the corpus cavernosum. The production of these conditions typically results in erection during sexual stimulation. In fact, studies indicate that as many as four out of five men suffering from impotence are restored sexual function when Viagra is taken, no matter what originally caused the dysfunction. Moreover, taken in pill form approximately an hour before sexual activity, Viagra is much less invasive than many earlier forms of treatment, such as pump devices, surgical implants, and suppositories.