UNLABELLED The myocardial uptake kinetics of 14(R,S)-[18F]fluoro-6-thia-heptadecanoic acid (FTHA) were evaluated in humans with PET. The relationship between human myocardial FTHA uptake kinetics and the rate-pressure product (RPP) as an index of myocardial oxygen consumption was investigated in seven normal subjects under fasting conditions. METHODS Seven studies were performed at rest and under submaximal continuous supine bicycle exercise with elevated RPP. An additional five studies were performed after dipyridamole injection to increase myocardial blood flow independent of the myocardial energy requirement. RESULTS In all studies, rapid tracer uptake was found within 2-3 min after injection, which remained nearly constant during the 30-min study. Patlak plots of myocardial FTHA kinetics showed a linear increase, indicating metabolic trapping. The mean uptake rate constant, Ki, obtained from Patlak plot analysis was 0.11 +/- 0.02 ml/g/min at rest and increased significantly to 0.26 +/- 0.06 ml/g/min during exercise. The dipyridamole study yielded a comparatively small elevation with a mean Ki of 0.15 +/- 0.02 ml/g/min, which was not significant in the analysis of variance and the Duncan range test. There was a significant correlation between Ki and RPP, with r = 0.85 (p < 0.01). CONCLUSION Analysis of FTHA uptake kinetics with PET may be useful for noninvasive assessment of myocardial utilization of exogenous long-chain fatty acids in general and of beta oxidation in the fasting state.