Patients with pulmonary arterial hypertension (PAH) have reduced health related quality of life (HRQOL) and impaired exercise capacity. Despite fourteen approved therapies, most patients die within ten years. Increasing physical activity is highly efficacious in PAH, resulting in six-minute walk distance (6MWD) and HRQOL improvement that often exceeds the effect of medications. Prior activity studies required inpatient rehabilitation, which is impractical, hard to sustain, and poorly scalable to a rare disease. The Investigators propose a randomized trial of smart texts versus usual care for 6 months. The Investigators will randomize 100 PAH patients to the mHealth intervention or usual care. The Investigators will test the effect of a text-based mHealth intervention on HRQOL in PAH using the PAH-specific emPHasis-10 questionnaire. The Investigators will also test the effect of an mHealth intervention on exercise capacity, measured by a supervised home-based 6MWD test. Finally, the Investigators will examine the effect of the intervention on time to clinical worsening (composite of PAH therapy escalation, PAH hospitalization, and death) one year after randomization.