Fildena 100 It belongs to the class of drugs known as PDE 5 inhibitors. It blocks the action of the PDE 5 enzyme (which inhibits blood flow) and improves blood circulation. When a person is s*xually stimulated, a chemical known as nitric oxide is released into the p*nis. Nitric oxide stimulates the production of cGMP by interacting with the heme group of the soluble enzyme guanylate cyclase (sGC). cGMP is responsible for the contraction and dilation of blood vessels. However, due to the attack of the PDE 5 enzyme, the cGMP is destroyed. The sildenafil citrate present in Fildena blocks the action of PDE 5 and allows the proper production of cGMP. This allows blood to flow easily to the penis. When cGMP is produced, more and more blood flows into the p*nis. This creates pressure and leads to an erection.