Glucose extraction by ischemic human myocardium was investigated at the time of diagnostic cardiac catheterization in 27 subjects who had fasted overnight. Paired arterial and coronary sinus blood samples, obtained before and during coronary sinus pacing, were analyzed for glucose and lactate. Pacing to a rate 50 to 70% greater than control or to the development of chest pain induced no significant change in the arterial level of either substrate. No correlation was noted between arterial level and myocardial extraction of either substrate at rest or during stress.Three groups of subjects were identified: group I: those with lactate extraction at rest and during pacing (n = 13); group II: those with lactate extraction at rest but production during pacing (n = 7); and group III: those with lactate production at rest with augmented production during pacing (n = 5). Two additional subjects produced lactate at rest but were not paced. Glucose extraction increased significantly with pacing tachycardia in group II (0.09 ± 0.03 mM to 0.26 ± 0.04 mM) and in group III (0.38 ± 0.17 mM to 0.58 ± 0.12 mM). No significant increase was noted in group I. A significant correlation was noted between glucose extraction and lactate production during pacing when groups II and III were combined (r = 0.81;P< 0.001).Myocardial ischemia in man was associated with augmented glucose extraction. The arterial glucose concentration was not a primary determinant of glucose extraction either before or during induced ischemia.