Machine of Action The physiologic device of erection of the penis involves unchain of nitric oxide (NO) in the corpus cavernosum during procreant stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), buy viagra online no prescriptionsbuy viagra online no prescription producing cagey flatten muscle relaxation in the corpus cavernosum and allowing inflow of blood. Sildenafil has no command relaxant effect on secluded human corpus cavernosum, but enhances the clout of nitric oxide (NO) by inhibiting phosphodiesterase genre 5 (PDE5), which is at fault for degradation of cGMP in the corpus cavernosum. When progenitive stimulation causes local rescue of NO, inhibition of PDE5 by sildenafil causes increased levels of cGMP in the corpus cavernosum, resulting in silky muscle relaxation and inflow of blood to the corpus cavernosum. Sildenafil at recommended doses has no truly in the absence of sexual stimulation. Studies in vitro require shown that sildenafil is picky for PDE5.