Hyperemia, which occurs immediately after coronary reperfusion, injures the myocardium. Mild coronary stenosis may mitigate this hyperemia and thus may augment myocardial salvage. To test this hypothesis, left anterior descending coronary arteries of dogs were occluded for 3 h. Then, reperfusion was permitted without residual stenosis (group A, n = 17) or with 75% stenosis (group B, n = 10). Regional myocardial blood flow (RMBF) was determined using colored microspheres. Dogs were sacrificed 1 week later to measure myocardial creatine kinase activity (CK) and for staining with triphenyl tetrazolium chloride (TTC). The RMBF measured 5 min after reperfusion increased significantly (inner layer, 171 +/- 16; outer layer, 165 +/- 11% of control) in group A. This hyperemia disappeared in group B (inner, 106 +/- 8; outer, 117 +/- 10% of control). However, the myocardial CK was more preserved (group A: inner, 31 +/- 4; outer, 44 +/- 4%; and group B: inner, 21 +/- 6; outer, 29 +/- 5%), and the infarct size was smaller in group A than in group B (group A: inner, 44 +/- 6; outer, 33 +/- 5; and group B: inner, 53 +/- 10; outer, 58 +/- 7% of the area at risk). We concluded that a residual stenosis of 75% at reperfusion abolishes the hyperemia but does not improve myocardial salvage.