A Pharmacokinetics Study for Pediatric Participants With Pulmonary Arterial Hypertension

Inclusion Criteria: * Currently have a diagnosis of PAH that is either: * idiopathic (including hereditary), related to collagen vascular disease, related to anorexigen use, associated with surgical repair, of at least 6 month duration, of a congenital systemic to pulmonary shunt (for example, atrial septal defect, ventricular septal defect, patent ductus arteriosus). * Have a history of the diagnosis of PAH established by a resting mean pulmonary artery pressure ≥25 mm Hg, pulmonary artery wedge pressure ≤15 mm Hg, and a pulmonary vascular resistance (PVR) ≥3 Wood units via right heart catheterization. In the event that a pulmonary artery wedge pressure is unable to be obtained during right heart catheterization, participants with a left ventricular end diastolic pressure \<15 mm Hg, with normal left heart function, and absence of mitral stenosis on echocardiography can be eligible for enrollment * Have a World Health Organization (WHO) functional class value of I, II or III at the time of enrollment Exclusion Criteria: * Have pulmonary hypertension related to conditions other than specified above, including but not limited to chronic thromboembolic disease, portal pulmonary hypertension, left-sided heart disease or lung disease and hypoxia * History of left-sided heart disease, including any of the following: * clinically significant (pulmonary artery occlusion pressure \[PAOP\] 15 to 18 mm Hg) aortic or mitral valve disease (that is, aortic stenosis, aortic insufficiency, mitral stenosis, moderate or greater mitral regurgitation) * pericardial constriction * restrictive or congestive cardiomyopathy * left ventricular ejection fraction \<40% by multigated radionucleotide angiogram (MUGA), angiography, or echocardiography * left ventricular shortening fraction \<22% by echocardiography * life-threatening cardiac arrhythmias * symptomatic coronary artery disease within 5 years of study entry as determined by the physician * History of atrial septostomy or Potts Shunt within 3 months before administration of study drug * Unrepaired congenital heart disease