Sildenafil citrate, one of the selective phosphodiesterase-5 (PDE5) inhibitors(IC50= 5.22 nM), is considered the best treatment for erectile dysfunction.
IC50 Value: 5.22 nM
Target: PDE 5
in vitro:  Pretreatment with 1 umol/L sildenafil potentiated the phosphorylation of ERK1/ERK2, an increase in the percentage of cells in S phase and cell proliferation, compared with serotonin stimulation alone (P < 0.05) . pretreatment of cells with sildenafilsuppressed serotonin-triggered activation of calcineurin/NFATc2 signaling pathway and resultant cyclin A expression, CDK2 activation and cell proliferation, while the presence of DT-3 [a specific protein kinase G (PKG) peptide inhibitor] reversed the effects of sildenafil on PASMCs.
in vivo: Sildenafil at a dose ranging from 10 to 40mg/kg statistically increased psychomotor seizure threshold in mice. Moreover, sildenafil enhanced the anticonvulsant action of all the studied AEDs in this test. Administration of oral sildenafil (45 mg·kg(-1)·day(-1)) had no effect on blood pressure in control rats but decreased pressure in RUPP rats (115 ± 1 mmHg; P < 0.05).
Toxicity: With a mean duration on tadalafil therapy of 243 ± 127 days at the time of analysis, 6MWD was unchanged. Patient-reported adverse events included headache (4%) and heartburn (2%). There was minimal change in BNP levels in the subset of patients receiving an ERA concomitantly.
Clinical trial: Sildenafil Impact on Ventricular Function in Patients With Heart Failure. Phase2/3

PDE
Pentoxifylline
PF-04447943
PF-2545920
Pimobendan
Roflumilast
Rolipram
Udenafil
Vardenafil
Vinpocetine
Zardaverine