This prospective, observational, multi-center, patient registry will follow patients who are newly initiated on Tyvaso for the treatment of Pulmonary Arterial Hypertension (PAH). Once enrolled, the patients' dose and titration will be followed for the first 6 months of treatment with Tyvaso.

A call-center will contact the patients directly at weeks 1, 2, 3, 4, 8, 12, 16, 20, and 24 to review their dose and titration schedule. In addition to patient-reported dosing data, some patient demographic information, will be collected by the investigative site at Baseline.

Inclusion Criteria:

• Are newly prescribed Tyvaso for the treatment of PAH and plan to initiate therapy
• Are willing and able to be contacted by the patient call center.

Exclusion Criteria:

• Have previously received Tyvaso.
• Are currently enrolled in an interventional (non-FDA approved) PH clinical trial.

Patients newly initiating on Tyvaso therapy for the treatment of PAH