Fildena 150 mg contains sildenafil citrate, a well-known medication for ED that has been thoroughly studied and proven effective. Sildenafil citrate works by blocking phosphodiesterase type 5 (PDE5), an enzyme that breaks down cyclic guanosine monophosphate (cGMP). By inhibiting PDE5, sildenafil helps raise cGMP levels, resulting in the relaxation of smooth muscle in the penis and better blood flow.