Mobile Health Intervention to Improve Exercise in Pediatric PH

Inclusion Criteria: * Adolescents between ages 10-21 years. * Diagnosed with WHO Group 1 PAH or WHO Group 4 PH (CTEPH) * WHO functional class I-III * 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. 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. * Functional class IV heart failure * Requirement of \> 2 diuretic adjustment in the prior three months. * Preferred form of activity is not measured by an activity tracker (swimming, yoga, ice skating, stair master, or activities on wheels such as bicycling or rollerblading). * Involved in any other investigational intervention.