Fildena 120 mg is a medication used to treat erectile dysfunction (ED) in men. It contains Sildenafil Citrate, the same active ingredient found in Viagra, which is a PDE5 inhibitor. Understanding the mechanism of action of Fildena 120 mg is essential for appreciating how it works to improve erectile function. Sildenafil Citrate, the active ingredient in Fildena 120 mg, works by inhibiting the action of the enzyme PDE5 (phosphodiesterase type 5). This enzyme is primarily found in the penis and is responsible for breaking down cGMP (cyclic guanosine monophosphate), a substance that plays a key role in muscle relaxation and blood vessel dilation.