Main Inclusion Criteria:
1. Confirmed diagnosis of Pulmonary Hypertension Group 1 (PAH).
2. PAH diagnosis at the time of baseline with the following RHC parameters: mPAP≥ 25 mmHg at rest, with a concomitant mPCWP, mLAP or LVEDP≤ 15 mmHg and a PVR≥240 dyn sec/cm -5.
3. The subject is receiving at least one approved PAH therapy and is clinically symptomatic from PAH.
4. Background PAH medication doses must be stable for at least 12 weeks prior to screening.
5. If on calcium channel blockade to treat PAH, must be on stable dose for at least 12 weeks prior to screening.
6. If on background conventional therapy, it must have been started at least 30 days prior to screening and on a stable dose for 30 days except for anticoagulation dose.
7. If previously treated with ERA, PDE-5 inhibitor, prostacyclin or a prostacyclin analog and is no longer on the treatment at screening, subject must be off the treatment for > 90 days.
8. If previously treated with calcium channel blocker as treatment for PAH and is no longer on treatment at screening, subject must be off treatment for > 90 days.
9. Age between 16 and 80 inclusive (our site will not enroll patients under 18)
10. Ideal body weight less than 99 Kg.
11. Subjects who in the opinion of the investigator will be able to use the INO pulse device continuously for 24 hours per day.
Main Exclusion Criteria:
1. Subjects with known HIV infection who have a history of or show any clinical or laboratory evidence of any opportunistic pulmonary disease (eg tuberculosis, other pneumonias) at the time of screening.
2. Any non-group 1 PAH, or PAH with significant venous or capillary involvement.
3. Left ventricular systolic or diastolic dysfunction, history of clinically significant valvular heart disease, or clinically signifcant cardiac ischemic disease.
4. Any subject who develops clinically significant rebound pulmonary hypertension following acute vasodilator testing during the baseline RHC defined as an increase in mPAP >50% from baseline value.