Inhibits cGMP specific phosphodiesterase type-5 (PDE5) in smooth muscle→ less cGMP breakdown→ more cGMP within vascular smooth muscle→ vascular smooth muscle relaxation→ vasodilation
Sildenafil
Acebutolol
Amlodipine
Bosentan
Hydralazine
Epoprostenol 
Tropicamide
Timolol