BACKGROUND: In patients with myocardial infarction (MI) and chronic stable angina, the coronary flow reserve (CFR) is reduced not only in the region of myocardium perfused by the ischemia-related artery but also in the regions supplied by angiographically normal coronary arteries. The effect of myocardial stunning on the remote CFR is unknown, however. METHODS: In ten open-chest anesthetized dogs, left circumflex coronary artery was occluded for 15 minutes (myocardial stunning group, n=5) or for 30 minutes (MI group, n=5) and was followed by a reperfusion for 60 minutes. Before coronary occlusion and at 30 minutes and at 60 minutes after reperfusion, resting coronary blood flow (CBF) and maximal CBF after IV injection of each of adenosine (ADE) and acetylcholine (Ach) was measured with electromagnetic flow probe located in the proximal left anterior descending coronary artery. CFR was calculated as the ratio of maximal and resting CBF. RESULTS: At 30 minutes and 60 minutes after reperfusion, the remote resting CBF were significantly increased in both groups and the remote CFR was significantly decreased in both groups. The CFR of the MI group was lower than myocardial stunning group. The coronary vasodilator response to Ach was significantly lower than the response to ADE in both groups. CONCLUSION: After MI and myocardial stunning, there was severe coronary vasodilator abnormality in the remote myocardium and that was more marked after MI. The coronary vasodilator response to Ach was significantly lower than the response to ADE in both groups, suggesting endothelial dysfunction in remote myocardium.