Pulmonary hypertension (PH) refers to abnormalities in the pulmonary vasculature associated with a diverse group of disorders. The World Health Organization (WHO) classifies pulmonary hypertension into five groups, with Group I comprising pulmonary arterial hypertension (formerly referred to as "primary pulmonary hypertension"). Although not currently a part of the WHO classification, exercise-induced pulmonary arterial hypertension (EIPAH), defined by normal pulmonary artery pressures at rest and elevation of pulmonary pressures with exercise, is increasingly recognized as a distinct clinical entity. In some patients, exercise-induced pulmonary hypertension may represent a precursor for developing an established elevation in pulmonary pressures at rest that defines PAH. Functional PET imaging has not previously been utilized to quantify perfusion and vascular compliance in patients with pulmonary arterial hypertension. The overall goal of this study is to evaluate regional lung perfusion, perfusion heterogeneity, and vascular compliance in patients with both exercise-induced and resting pulmonary hypertension using functional positron emission tomography imaging. Ultimately, if quantifiable differences between healthy subjects and patients with PAH are detected with 13NN and 11CO labeled PET, functional PET imaging may provide a useful imaging modality in early diagnosis of pulmonary hypertension and monitoring response to therapy. In this pilot study, we will recruit 10 adult patients with pulmonary hypertension (5 with PAH and 5 with EIPAH) who are on stable PAH-specific therapy (if any), and 5 healthy controls.