 Originally created as a treatment for high blood pressure in 1989, it was found to have a secondary use as an effective PDE5 inhibitor, enabling men who use it to gain stronger erections after arousal.The FDA approved Viagra on March 27, 1998.Discovered by Pfizer, sildenafil is a potent and selective inhibitor of cGMP-specific phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum in the penis.