As mentioned earlier the active pharmaceutical ingredient of Fildena 100 is Sildenafil citrate, the popular drug market as Viagra by Pfizer. Sildenafil was first discovered by Pfizer in  for the treatment of heart-related chest pain. It was accepted for medical use in the US and Europe in . In 2017 its patent expired and generic versions started to come out. It works by deactivating an enzyme present in our body called PDE5 or phosphodiesterase – 5 which causes increased blood flow in the p*nis and is able to cause long and sustained erection in males.