CarbolinesSulfonesPurinesPhosphodiesterase 5 InhibitorsPiperazinesPhosphodiesterase InhibitorsCyclic Nucleotide Phosphodiesterases, Type 5Erectile Dysfunction3',5'-Cyclic-GMP PhosphodiesterasesVasodilator AgentsPenile ErectionHypertension, PulmonaryImpotence, VasculogenicCyclic GMPPenisPhosphoric Diester HydrolasesPyrimidinonesAdministration, OralTriazinesPulmonary ArteryPriapismCross-Over StudiesDouble-Blind MethodNitric OxideClitorisCyclic GMP-Dependent Protein KinasesHypertrophy, Right VentricularPulmonary Wedge PressureVascular ResistanceDihydroergocristineTreatment OutcomeDose-Response Relationship, DrugIloprostPapaverineHemodynamicsEjaculationDrug Therapy, Combination