This study measured glucose uptake in the right ventricle (RV) of patients with pulmonary hypertension and investigated the relationship to hemodynamics and survival. Myocardial 18F-fluorodeoxy-glucose (FDG) uptake was measured using single-photon positron emission tomography (SPECT) in 24 patients with idiopathic pulmonary arterial hypertension (IPAH) and 43 patients with congenital heart disease (CHD). In both IPAH and CHD-PAH, RV FDG uptake (RV/LV ratio) was associated with pulmonary vascular resistance (PVR). A second SPECT scan was performed in nine patients after 6 months treatment with sildenafil. PVR decreased from 1683±426 to 1207±383 dyn s−1 cm−5 (P < 0.05) and cardiac index improved from 2.2±0.2 to 2.8±0.5 L/min/m2 (P < 0.01). RV/LV FDG uptake decreased from 1.28±0.32 before treatment to 0.99±0.23 (P < 0.05). Survival in the IPAH group with a baseline RV/LV FDG uptake greater than the median value of 1.20 was significantly lower than that of the group with RV/LV FDG uptake below 1.20 (log-rank test, P < 0.05). In contrast, baseline RV/LV FDG was of little informative value in CHD. FDG uptake by the RV reflects the severity of PVR in PAH. Increased RV FDG uptake is a marker of poor prognosis in IPAH and is reduced in patients receiving effective therapy. It could prove useful in the early clinical assessment of novel therapies for PAH.