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.