Source:http://linkedlifedata.com/resource/umls/id/C0724693
NCI: The citrate salt of a pyrazolopyrimidinone derivative structurally related to zaprinast. Sildenafil selectively inhibits cyclic guanosine monophosphate (cGMP)-specific type 5 phosphodiesterase, resulting in vasodilation in the corpus cavernosum of the penis and penile erection. (NCI04)