Right Ventricular Pacing in Pulmonary Arterial Hypertension

Inclusion Criteria: * Patients referred for a clinically indicated right heart catheterization to either diagnose pulmonary arterial hypertension prior to initiating therapies or monitor response to ongoing therapies in patients with diagnosed pulmonary arterial hypertension. * Patients with pulmonary arterial hypertension with or without significant right ventricular dysfunction as assessed by baseline echocardiography and standard of care right heart catheterization * Functional class 2 or 3 symptoms * Are able to undergo cardiac MRI, endocardial mapping, and pressure volume measurements * English speaking * All patients will be required to have evidence of right ventricular hypertrophy or conduction delay (QRS \> 130ms) on surface ECG Exclusion Criteria: * Preexisting left bundle branch block, current atrial fibrillation, or pacemaker/ defibrillators * Functional class 4 symptoms * Patients treated with parenteral or subcutaneous therapies for pulmonary hypertension * Contraindication to right heart catheterization including significant thrombocytopenia (platelets \< 50,000), coagulopathy (INR \> 1.8), or pregnancy as determined by routine screening laboratory work * Mean pulmonary artery pressure less than 25 mmHg as determined by the right heart catheterization on the day of the study procedure * Pulmonary capillary wedge pressure greater than or equal to 15 mmHg as determined by the right heart catheterization on the day of the study procedure * Severe tricuspid regurgitation as determined by baseline transthoracic echocardiogram. * Left ventricular dysfunction (EF \< 50%) as determined by baseline transthoracic echocardiogram. * Inability to complete cardiac MRI or transthoracic echocardiography * Patients with confounding systemic disease specifically portopulmonary hypertension and scleroderma associated pulmonary hypertension * Patients otherwise deemed not appropriate for the study as determined by the study investigators