Zaprinast is a cGMP-specific PDE inhibitor which moderately inhibits PDE5 and PDE6. It weakly inhibits PDE9, PDE10 and PDE11. Sildenafil (Viagra™) was developed from Zaprinast, which enhances the vasodilatory effects of nitric oxide in a range of vascular tissues by prolonging the cGMP-mediated activation of cGMP-dependent protein kinase. Also, GPR35 is activated by Zaprinast.