Inclusion Criteria:

• Diagnosed with idiopathic, heritable, scleroderma, or drug- or toxin-associated pulmonary arterial hypertension (PAH) according to World Health Organization consensus recommendations.
• Repaired simple congenital heart disease or unrepaired ASD.
• Stable PAH-specific medication regimen for three months prior to enrollment. Subjects with only a single diuretic adjustment in the prior three months will be included. Adjustments in IV prostacyclin for side effect management are allowed.
• Subjects must own a Bluetooth-capable modern smartphone capable of receiving and sending text messages and an active data plan.
• FEV1 > or = 60% predicted and no more than mild abnormalities on lung imaging.
• WHO Functional Class I-III.
• Ambulatory.

Exclusion Criteria:

• Prohibited from normal activity due to wheelchair bound status, bed bound status, reliance on a cane/walker, activity-limiting angina, activity-limiting osteoarthritis, or other condition that limits activity.
• Pregnancy.
• Diagnosis of PAH etiology other than idiopathic, heritable, or associated with drugs or toxins.
• Drug and toxin associated PAH patients with active drug use.
• WHO Functional class IV heart failure.
• FEV1 > or = 65% predicted AND normal chest imaging.
• WHO Functional class IV heart failure.
• Requirement of > 1 diuretic adjustment in the prior 30 days.
• Preferred form of activity is not measured by an activity tracker (swimming, ice skating, stair master, or activities on wheels such as bicycling or rollerblading).
• Type I diabetes mellitus.
• Prior diagnosis of cirrhosis.
• Untreated hypo- or hyper-thyroidism.
• eGFR by MDRD < 40mL/min.

Eligibility last updated 1/7/22. Questions regarding updates should be directed to the study team contact.