Background. Measurements of the rate of myocardial glucose utilization (rMGU) play a key role in the assessment of alterations in myocardial substrate metabolism in normal and abnormal cardiac states. In this study we determined whether rMGU could be quantified by positron emission tomography (PET) and 1-carbon-11-glucose. Methods and Results. Twenty dogs were studied with a variety of interventions including fasting (n = 5), hyperinsulinemic-euglycemic clamp at rest (n = 6), clamp and phenylephrine (n = 5), and clamp and dobutamine (n = 4). Measurements of myocardial blood flow and rMGU were made by PET with oxygen-15-water and 1-C-11-glucose, respectively. Arterial-coronary sinus sampling was performed to measure rMGU by the Fick method. Values for rMGU ranged from 50 to 2436 nmol/g/min. Myocardial 1-C-11-glucose images of high quality were obtained. There was a close and direct correlation between values for rMGU measured by PET and those measured directly (y = 0.86x + 112, r = 0.98, P <.0001). The coefficient of variation for the regional estimates of rMGU ranged from 11.3% ± 7.4% during clamp at rest to 16.3% ± 8.4% during clamp with phenylephrine. Conclusions. It now appears possible to quantify myocardial glucose utilization by PET with 1-C-11-glucose. This method should become a valuable tool in the assessment of alterations in myocardial glucose metabolism in both normal and abnormal myocardium.