Fildena 150mg blocks the breakdown of cyclic guanosine monophosphate (CGMP) in smooth muscle cells that line blood vessels that supply the main swelling tissue of the penis. Sildenafil citrate helps to increase the action of nitrogen monophosphates by inhibiting PDE-5 (phosphodiesterase 5), which breaks down CGMP and cyclic guanosine monophosphates (nitric oxide) in the penis blood vessels.