Vardenafil is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5) and an oral therapy for the treatment of erectile dysfunction. During sexual stimulation, nitric oxide (NO) is released from nerve endings and endothelial cells in the corpus cavernosum, activating the enzyme guanylate cyclase and increasing the synthesis of cGMP in the smooth muscle cells of the corpus cavernosum.