Idiopathic pulmonary arterial hypertension (IPAH) results in increased right ventricular (RV) workload and oxygen demand. It has been shown that myocardial oxygen consumption (MVO 2 ) of the hypertrophied right ventricle of IPAH patients can be measured using PET and 15 O-labeled tracers. This method is, however, not very suitable for routine clinical practice. The purpose of the present study was to assess whether MVO 2 can also be determined in the right ventricle of IPAH patients from the clearance of 11 C-acetate, a simple method that is in use for MVO 2 measurements of the left myocardium. Methods: Seventeen of 26 IPAH patients performed the total PET study. Nine other patients were scanned only for 11 Cacetate. 15 O-H 2 O, 15 O-O 2 , and 15 O-CO scans were used to derive RV flow, oxygen extraction fraction, and blood volume, respectively, from which RV MVO 2 was calculated. The rate of clearance determined by monoexponential curve fitting (K mono ) and the efflux rate constant k 2 were derived from the 11 C-acetate scan. The RV ratepressure product was also determined by means of right heart catheterization, as an index of the RV MVO 2 , and was calculated as the product of systolic pulmonary artery pressure and heart rate. Results: Both 11 C-acetate clearance rates, K mono (R 2 5 0.41, P 5 0.006) and k 2 (R 2 5 0.45, P 5 0.003), correlated with RV MVO 2 . They also correlated with RV rate-pressure product (K mono , R 2 5 0.41, P 5 0.0005; k 2 , R 2 5 0.48, P , 0.0001). Conclusion: 11 C-acetate clearance rates correlated moderately with quantitative RV MVO 2 measurements in IPAH. Therefore, 11 C-acetate PET can be used only as an index of RV oxidative metabolism in IPAH patients. The oxygen consumption (MVO 2 ) of the normal right myocardium is less than that of the left heart as a result of a lower afterload (1). In idiopathic pulmonary arterial hypertension (IPAH), elevated pulmonary vascular resistance causes right ventricular (RV) hypertrophy and ultimately fatal RV failure. To gain insight on the pathophysiology of reduced pump function in the failing heart, quantification of MVO 2 is important. A noninvasive method using state-of-the-art PET and 15 O-labeled tracers has been validated as a means to measure MVO 2 accurately (2-4). Using this method, it was recently demonstrated that the right ventricle consumes more oxygen in patients with severe IPAH than in those with mild PAH for generating similar RV power output (5). This method is, however, extensive and time-consuming (4), requiring 3 consecutive PET scans ( 15 O-H 2 O, 15 O-CO, and 15 O-O 2 ) and an on-site cyclotron to produce the short-lived 15 O tracers (6). PET using 11 C-acetate has been proposed as a more practical method to estimate MVO 2 . With 11 C-acetate being the precursor of acetyl-CoA in the tricarboxylic acid cycle, the rate of 11 C-acetate clearance determined by monoexponential curve fitting (K mono ) is closely related to MVO 2 of the left heart (4,7-10).It is not known, however, whether 11 C-acetate can also be used to esti...