PDE5 inhibitors are used as potent pulmonary vasodilators reducing Pulmonary hypertension 4 and inhibiting vascular remodelling. L region: the methyl piperazine group (see figure 4) of Fildena is surrounded by Tyr 664, Met 816, Ala 823 and Gly 819 residues, and residues 662-664 form a lid over the pocket narrowing the entrance to the active site of PDE5. Q pocket: it is believed that the guanidine