The phosphodiesterase inhibitor tetrahydrophthalazinone NPD-008 was explored by phenotypic in vitro screening, target validation, and ultrastructural approaches against Trypanosoma cruzi . displayed activity different forms strains of T. (50% effective concentration [EC 50 ], 6.6 to 39.5 μM). Increased cAMP levels its combination with benznidazole gave synergistic interaction.