Fildena 100 mg is a PDE5 inhibitor, which works by blocking the enzyme that limits blood flow to the penis. This enhances the effects of nitric oxide, relaxing blood vessels in the penile area, and allowing increased blood flow to enable an erection.Onset and Duration: Fildena 100 mg typically takes effect within 30–60 minutes and lasts for about 4–6 hours. However, it requires sexual arousal to be effective.