BACKGROUND AND OBJECTIVES: Patients with chronic diabetes mellitus (DM) have an increased risk of cardiac dysfunction and mortality. There is some evidence that suggests acute hyperglycemia may cause vascular dysfunction. However, it is unknown whether acute, short-term hyperglycemia affects coronary microcirculation function in healthy subjects. The present study was undertaken to explore this issue. SUBJECTS AND METHODS: We evaluated 20 healthy males who had no history of DM or impaired glucose tolerance, ranging in age from 23 to 36 years (25.9+/-3.3 years). We checked blood sugar, 12-lead electrocardiography, pulse wave velocity, and coronary flow reserve using echocardiography during fasting, and 30, 60, 90, and 120 minutes after ingestion of 75 g of glucose orally. RESULTS: Non-significant prolongation of the QTc dispersion was observed after the 75 g glucose loading. No significant difference in the pulse wave velocity of the carotid-to-femoral artery, carotid-to-radial artery, or femoral-to-dorsalis pedis artery was observed after the 75 g glucose loading. There was a significant reduction in the coronary flow reserve at 60 (4.06+/-0.75 vs. 3.54+/-0.82, p=0.021) and 90 minutes (4.06+/-0.75 vs. 3.59+/-0.63, p=0.021) after the 75 g glucose loading compared to that on fasting. CONCLUSION: The results of this study suggest that acute exposure to high circulating glucose levels does not affect heterogeneity of the ventricular repolarization or arterial stiffness, but it does reduce the coronary flow reserve in healthy young men.