1. Male or female, 18-75 years old. 
2. Has a diagnosis of WHO Group 1 PAH. 
3. Right heart catheterization performed at Screening with results that are: 
1. Mean pulmonary arterial pressure ≥25 mmHg (at rest) and 
2. Pulmonary venous hypertension (measured as pulmonary capillary wedge pressure (PCWP) ≤15 mmHg. If PCWP is not available, then mean left atrial pressure or left ventricular end-diastolic pressure ≤15 mmHg in the absence of left atrial obstruction. and 
3. Pulmonary vascular resistance (PVR) ≥300 dyn•s/cm5 (3.75 Wood units) 
4. Has WHO/NYHA-FC of II or III. 
5. Be on stable dose of at least one of the following PAH-specific therapies: endothelin receptor antagonist, an agent acting on the nitric oxide pathway (phosphodiesterase type 5 inhibitor or soluble guanylate cyclase stimulator), and/or a prostacyclin or prostacyclin analog. 
6. Has a 6-minute walk distance that is ≥150 and ≤500 meters. 
7. Have a ventilation-perfusion scan that rules out thromboembolic disease. 

NCT02664558_inc_T11
Person
Male
NCT02664558_inc_T12
Person
female
NCT02664558_inc_T13
Value
18-75 years
NCT02664558_inc_T14
Person
years old
NCT02664558_inc_T15
Measurement
WHO Group
NCT02664558_inc_T16
Value
1
NCT02664558_inc_T17
Condition
PAH
NCT02664558_inc_T18
Procedure
Right heart catheterization
NCT02664558_inc_T20
Temporal
performed at Screening
NCT02664558_inc_T21
Reference_point
Screening
NCT02664558_inc_T22
Measurement
Mean pulmonary arterial pressure
NCT02664558_inc_T23
Value
≥25 mmHg
NCT02664558_inc_T24
Qualifier
at rest
NCT02664558_inc_T25
Condition
Pulmonary venous hypertension
NCT02664558_inc_T26
Measurement
pulmonary capillary wedge pressure (PCWP)
NCT02664558_inc_T27
Value
≤15 mmHg
NCT02664558_inc_T28
Condition
mean left atrial pressure
NCT02664558_inc_T29
Condition
left ventricular end-diastolic pressure
NCT02664558_inc_T30
Value
≤15 mmHg
NCT02664558_inc_T31
Negation
absence
NCT02664558_inc_T32
Condition
left atrial obstruction
NCT02664558_inc_T33
Condition
Pulmonary vascular resistance (PVR)
NCT02664558_inc_T34
Value
≥300 dyn•s/cm5
NCT02664558_inc_T35
Value
3.75 Wood units
NCT02664558_inc_T36
Measurement
WHO/NYHA-FC
NCT02664558_inc_T37
Value
II
NCT02664558_inc_T38
Value
III
NCT02664558_inc_T39
Scope
II or III
NCT02664558_inc_T40
Qualifier
stable dose
NCT02664558_inc_T41
Multiplier
at least one
NCT02664558_inc_T42
Procedure
PAH-specific therapies
NCT02664558_inc_T43
Drug
endothelin receptor antagonist
NCT02664558_inc_T44
Drug
agent acting on the nitric oxide pathway
NCT02664558_inc_T45
Drug
phosphodiesterase type 5 inhibitor
NCT02664558_inc_T46
Drug
soluble guanylate cyclase stimulator
NCT02664558_inc_T47
Scope
phosphodiesterase type 5 inhibitor or soluble guanylate cyclase stimulator
NCT02664558_inc_T48
Drug
prostacyclin analog
NCT02664558_inc_T49
Drug
prostacyclin analog
NCT02664558_inc_T50
Scope
endothelin receptor antagonist, an agent acting on the nitric oxide pathway (phosphodiesterase type 5 inhibitor or soluble guanylate cyclase stimulator), and/or a prostacyclin or prostacyclin analog
NCT02664558_inc_T51
Measurement
6-minute walk distance
NCT02664558_inc_T52
Value
≥150 and ≤500 meters
NCT02664558_inc_T53
Procedure
ventilation-perfusion scan
NCT02664558_inc_T54
Condition
thromboembolic disease
NCT02664558_inc_T56
Negation
rules out