Fildena 50 mg contains sildenafil citrate, a phosphodiesterase type 5 (PDE5) inhibitor. It works by blocking the enzyme PDE5, which normally breaks down cyclic guanosine monophosphate (cGMP) in the body. cGMP plays a crucial role in relaxing the smooth muscle tissue in the penis. When PDE5 is inhibited, cGMP levels increase, leading to the relaxation of smooth muscle cells in the blood vessels of the penis. This allows for increased blood flow, helping to achieve and maintain an erection in response to sexual stimulation. The drug specifically targets the penis, with minimal effects on other parts of the body.