RecruitingDevice studyMobile Health Intervention to Improve Exercise in Pediatric PHChildren and adults with pulmonary arterial hypertension (PAH) have severely reduced daily activity compared to healthy populations. In adults, investigators recently demonstrated that lower baseline daily step counts associated with increased risk of hospitalization and worsening WHO functional class; similarly, reduced step counts associate with hospitalization in children with PAH. This application builds on our recently completed NIH-funded pilot mobile health (mHealth) trial in adult patients with PAH which demonstrated the ability to remotely increase step counts. The investigators now aim to: (1) adapt our mHealth intervention to the developmental needs and interests of adolescents; and, (2) determine if our intervention increases step counts in adolescents, providing the foundation for a larger trial to assess the impact on quality of life and clinical outcomes.