- Subjects must have persistent symptoms due to PAH despite therapy with at least one of the following PAH medications: an endothelin receptor antagonist, asoluble guanylate cyclase stimulator or a phosphodiesterase inhibitor. The subjects' PAH medication regimen, with typical medications including calcium channel blockers, endothelin receptor antagonists, soluble guanylate cyclase stimulators and/or phosphodiesterase inhibitors, must have been used at a stable dose and frequency for at least 12 weeks before the screening visit and during the screening period.