Its action is similar to the action of nitric oxide, which is a potent vasodilator, especially for the venules, besides being an inhibitor of platelet aggregation. During pregnancy, nitric oxide is synthesized in in utero-placental tissues and endothelial cells, helping to maintain low vascular resistance in the utero- and fetoplacental circulations. Phosphodiesterase metabolizes cyclic guanosine monophosphate; therefore, phosphodiesterase type 5 inhibition leads to cyclic guanosine monophosphate increase with associated vasodilation, independently of nitric oxide. Therefore, phosphodiesterase type 5 inhibitors have the potential to achieve similar therapeutic goals when compared with nitric oxide.