A Pilot Study of Microbiota Transplant With Antibiotic Preconditioning and Fiber Supplementation in Pulmonary Arterial Hypertension (GUT RESTORE-PAH)

Inclusion Criteria: * Provision of signed and dated consent form * Ages 18-75 * Diagnosis of PAH * On stable treatment for PAH for one month prior to enrollment * Able to swallow capsules * Able to provide blood sample and fecal sample * Stated willingness to comply with all study procedures and availability for the duration of trial to follow-up by telephone, in-person, email, and/or video visits or correspondence. Exclusion Criteria: * Dysphagia to pills * Clinically active inflammatory bowel disease * Pregnancy or breastfeeding. A pregnancy test will be obtained from females of child- bearing potential at the screening visit or day 1 (prior to the receipt of MTT). Patients with a positive pregnancy test will be excluded. A negative result will be required for subjects who are females of child-bearing potential to receive MTT. Patients will be counseled to avoid pregnancy which is the standard of care for patients with PAH. * Life expectancy of \< 6 months * Presence of ileostomy or colostomy * Patients on immunosuppressants (calcineurin inhibitors, prednisone ≥ 20 mg/day, methotrexate, azathioprine, immunosuppressive biologics, JAK inhibitors). * Patients with neutropenia (an absolute neutrophil count \< 0.5 x 10 9 cells/L) obtained on a complete blood count with differential at screening * History of solid organ or bone marrow transplant * Anticipated recurrent antibiotic use (patients with frequent urinary tract infections or sinusitis) * History of severe anaphylactic food allergy * History of celiac disease * Patients receiving cancer chemotherapy, immunotherapy, or radiation * Patients with severe Irritable bowel syndrome (IBS) defined by an IBS score \>250