Vardenafil, the active ingredient in Zhewitra 60 mg, works by inhibiting the enzyme phosphodiesterase type 5 (PDE5). By blocking PDE5, Vardenafil helps to increase the levels of cyclic guanosine monophosphate (cGMP), a chemical that relaxes smooth muscles in the blood vessels of the penis. This relaxation allows for increased blood flow into the penis during sexual stimulation, leading to an erection.