Increased blood flow to the penis, which is required to get and maintain an erection, is how Fildena 100mg works. When a man is excited sexually, the arteries in his penis relax and enlarge. This increases blood flow to the sponge-like corpus cavernosum tissue. Fildena 150mg primary component is sildenafil citrate, a PDE5 inhibitor. It aids in the inhibition of the enzyme that degrades cGMP.