Prior human studies evaluating response to PH-specific therapies focused only on the right ventricle. Oikawa et al. looked at the RV uptake in patients with PH and evaluated them before and after treatment with epoprostenol. Fang and colleagues used FDG-SPECT evaluate FDG uptake in the RV of patients with IPAH and PH before and after treatment with sildenafil. Both of those studies used SUV (specific uptake variable). The investigators propose to focus on the lung and the RV uptake rate (Ki) in order to provide a more robust analysis of the metabolic changes that underlie the development of pulmonary hypertension both in the right ventricle and the lung parenchyma, and to study the response to ambrisentan with FDG-PET.