Assessmet of Patients With PAH Right Ventricular Volume

Inclusion Criteria: * Patients with Group 1 Pulmonary Arterial Hypertension * IPAH * HPAH * APAH-CTD * APAH-HIV * APAH-PoPH * APAH-Drugs/Toxins * APAH-CHD repaired simple systemic to pulmonary shunts, i.e. ASD, VSD and/or PDA * APAH-CHD unrepaired simple systemic to pulmonary shunts, i.e. ASD, VSD and/or PDA Patients who can be expected to lie motionless during imagine Males and females 12 years of age and older Exclusion Criteria: * Lack of informed consent (and assent as appropriate) * Other forms of PH not included in inclusion criteria * Left heart disease including clinically significant valvular disease, ,i.e. moderate or greater mitral regurgitation or stenosis or mild or greater aortic insufficiency or stenosis, pericardial disease, LV systolic dysfunction, i.e. LVEF \<40% or LVSF \<22%, and/or clinically significant LVDD * Known/detected arrhythmia that interferes with image acquisition * Implanted cardiac defibrillator, pacemaker, or other devices containing ferromagnetic materials * Pregnant or breast-feeding females * Contraindications for MRI (for those patient that undergo MRI) * Clinically significant obstructive or restrictive lung disease * Subjects with known HIV infection who have any clinical or laboratory evidence of any opportunistic pulmonary disease (e.g., tuberculosis, Pneumocystis carinii pneumonia, or other pneumonias) * PAH associated with thyroid disorders, glycogen storage disease, Gaucher's disease, hereditary hemorrhagic telangiectasia, hemoglobinopathies, myeloproliferative disorders or splenectomy * Any subjects with congenital heart disease other than the simple congenital to systemic shunts specified in the inclusion criteria * PAH associated with significant venous or capillary involvement (PCWP ˃ 15 mmHg), known pulmonary veno-occlusive disease, or pulmonary capillary hemangiomatosis * Clinically significant cardiac ischemic disease * Systemic hypertension defined as SBP ˃ 160 mmHg and/or DBP ˃ 95 mmHg (treated or untreated) * Moderate or severe hepatic impairment, i.e., Child-Pugh Class B or C * Any subject with obstructive sleep apnea or who requires the use of CPAP or BiPAP device