The investigators propose to study the relationship between right ventricle (RV) steatosis and RV function, exercise capacity, and outcomes in humans with pulmonary arterial hypertension (PAH) and to identify potential drivers of lipid accumulation.

The investigators propose to test the hypothesis that abnormal lipid metabolism in PAH leads to delivery of fatty acids in excess of RV oxidative capacity, resulting in steatosis and lipotoxicity. The objectives of the study are to: 1) Define the relationships between RV steatosis, RV function, and exercise capacity; 2) Identify mechanistic drivers of RV steatosis including BMPR2 expression and lipid metabolism; 3) Examine lipid metabolism in PAH skeletal muscle as a potential driver of reduced functional capacity.

In Aim 1 (clinical relevance) the investigators will measure RV and left ventricle (LV) lipid in participants with heritable, idiopathic, and scleroderma- associated PAH. Participants will undergo the 6-minute walk test, cardiopulmonary exercise testing, and will be followed for clinical events. A subgroup will undergo repeat MRS at four timepoints over three years to determine the natural history of steatosis.

In Aim 2 (mechanism), the investigators will perform metabolomic/lipidomic profiling of peripheral and coronary sinus plasma and measure BMPR2 expression to identify potential drivers of steatosis.

In Aim 3 (specificity), the investigators will perform MRS on skeletal muscle in Aim 1 participants and matched healthy controls to clarify the systemic effects of lipid metabolic defects in PAH.

Inclusion criteria:

• ≥ 18 years old
• Diagnosed with idiopathic, heritable, connective tissue disease-associated PAH, associated pulmonary arterial hypertension (PAH), or drug-or toxin-associated PAH according to World Health Organization (WHO) consensus recommendations.
• Stable PAH-specific medication regimen for three months prior to enrollment. Adjustments in IV prostacyclin for side effect management are allowed. Diuretic adjustments are permitted.
• WHO Functional Class I-III
• Ambulatory
• Able to have an MRI/MRS, perform a 6MWD test, and cardiopulmonary exercise test

Exclusion criteria:

• Pregnancy
• Diagnosis of PAH etiology other than idiopathic, heritable, connective tissue disease - associated PAH or associated with drugs and toxins
• WHO Functional class IV heart failure
• Requirement for continuous oxygen
• Unable to have an MRI/MRS, perform a 6MWD test, or cardiopulmonary exercise test.
• Patients with implanted/embedded ferromagnetic material that would preclude cardiac MRI

Patients with PAH will be recruited from the Center for Pulmonary Vascular Disease (CPVD) at Vanderbilt University Medical Center.