Fildena 100 mg is a medication used to treat erectile dysfunction (ED) in men. It contains the active ingredient sildenafil citrate, which belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. When a man is sexually aroused, nitric oxide is released in the body, which in turn increases the production of cyclic guanosine monophosphate (cGMP). cGMP is responsible for relaxing the smooth muscles in the blood vessels of the penis, allowing more blood to flow into it, resulting in an erection. However, in men with ED, the enzyme PDE5 breaks down cGMP prematurely, leading to difficulties in achieving and maintaining an erection.