The PDE5 enzyme, which controls blood flow in the penis, is inhibited by the drug. The release of nitric oxide during sexual excitement stimulates the production of cyclic guanosine monophosphate (cGMP) in the erectile tissue. cGMP causes smooth muscle relaxation and enhanced blood flow. The way Fildena 200 works is by blocking PDE5, which stops the breakdown of cGMP. This improves erectile function and prolongs muscular relaxation.