Purpose

- Evaluate for accuracy and reproducibility of data collected via the participant-operated Walk.Talk.Track. (WTT) app combined with Apple Watch during in-clinic, technician proctored 6MWT's. - Determine whether the WTT app on the Apple Watch can accurately collect information on distance traveled and heart rate (HR) during in-clinic 6MWT run by American Thoracic Society (ATS) guidelines - Determine whether participants can operate the WTT app and Apple Watch effectively to gather accurate data in a monitored and home-based setting - Prospectively monitor for changes in WTT app recorded 6MWT results following initiation of therapy in a treatment naïve cohort of PAH participants - Evaluate whether changes from baseline in 6 minute walk distance (6MWD) and heart rate recovery at one minute (HRR1) as well as other variables that have been associated with disease severity in PAH and left-sided heart disease (resting HR, heart rate variability [HRV], chronotropic index [CI]) can be identified before the 12-week follow up when comparing the treatment arm and the control arm - Evaluate whether changes from baseline in the HRR1, resting HR, HRV and/or CI are more evident in treatment responders when compared to treatment non-responders.