The overarching goal of this study is to examine the acute vasoreactive response to both inhaled nitric oxide and inhaled epoprostenol across both traditionally and non-traditionally interrogated phenotypes in PH, and to further characterize the relationship of vasoreactivity to disease severity and PH phenotype.

Inclusion Criteria:

• mPAP ≥ 21mmHg, PAWP ≤ 25mmHg, and PVR ≥3 WU
• Classified as WHO group I-III pulmonary hypertension

Exclusion Criteria:

• WHO group IV and V pulmonary hypertension
• Patients who are on baseline pulmonary vasodilator medications
• Severe aortic or mitral valve disease
• Patients who are pregnant
• Left ventricular ejection fraction of <35%
• Patients who are hospitalized as inpatients at the time of RHC
• Patients with systolic blood pressure <90mmHg or mean arterial pressure of < 60mmHg

Once study completion achieved