The purpose of this study is to evaluate patterns of metabolic activity in the heart of patients with pulmonary arterial hypertension(PAH). Patients with PAH are at risk of developing weakness or failure of the right side of the heart.It is possible that there is a relationship between the development of heart failure and the way the heart uses energy sources, such as sugar. This study is designed to evaluate the way the heart uses sugar uptake in patients with PAH using positron emission tomography(PET imaging)