Filitra 40 mg works by blocking the PDE5 enzyme, which is responsible for the breakdown of cyclic GMP (cGMP), a molecule that helps relax the smooth muscles in the blood vessels of the penis. By inhibiting PDE5, Filitra 40 mg allows cGMP to remain active for a longer period, facilitating better blood flow to the penis during sexual arousal. This improved circulation helps men with ED to achieve and sustain an erection, making it easier to engage in sexual activity.