Background Recent studies have shown that a global flow abnormality affects the entire coronary tree in patients with acute coronary syndrome (ACS), and that it is associated with adverse outcomes. Postprandial hyperglycemia is also thought to promote coronary endothelial dysfunction, as well as the release of inflammatory and vasoconstrictive factors. This study used the corrected Thrombolysis In Myocardial Infarction frame count (CTFC) to investigate whether optimal control of postprandial hyperglycemia improves pan-coronary flow. Methods and Results Eighty ACS patients with postprandial hyperglycemia who had successful coronary intervention and who had undergone a 75-g oral glucose tolerance test (OGTT) were included. A second OGTT and angiogram were performed 8 months after procedures. The patients were divided according to postprandial glycemia after the second 75-g OGTT; optimal postprandial hyperglycemia was defined as a 2-h blood glucose concentration <7.8 mmol/L. Changes in the CTFC of culprit/non-culprit arteries, glucose response, and other clinical variables were compared. Forty patients improved to an optimal control at 8 months. In the culprit artery, the 8-month angiogram revealed a significantly improved CTFC among those with optimal control compared with the initial angiogram (30±9 vs 24±12, p<0.05). In contrast, the CTFC was not evidently improved among patients with suboptimal control. The CTFC at 8 months had thus obviously improved more in patients with optimal, than with suboptimal control (24±12 vs 30±11, p<0.05). Conclusion Optimal control of postprandial hyperglycemia improves epicardial blood flow in both arteries and this beneficial effect might be from improved coronary endothelial function. (Circ J 2007; 71: 1079 - 1085)