...surrounding veins and traps the blood inside. The gas nitric oxide is essential to this muscle relaxation. Viagra (sildenafil citrate) works by blocking an enzyme called phosphodiesterase, which breaks down cyclic GMP, which is essential to the...

...that about 225,000 U.S. physicians have prescribed the impotence drug. Pfizer scientists in Britain developed sildenafil citrate -- the chemical name for Viagra -- as a heart medication, but that use wasn't successful. They soon realized...

...male and female rats, which plays a key role in supplying blood to erectile tissue, Dr. Allahdadi said. Using sildenafil citrate, otherwise known as Viagra, and two other erectile dysfunction drugs, the researchers were able to get a response...

...Viagra might have some aid perhaps with some female sexual problems," Dr. Lewis said. Chemical reactions Viagra (sildenafil citrate) works on the complex chemical reaction that allows a man to achieve an erection. Within the penis, a layer of...