We studied the importance of reflow after reperfusion for myocardial salvage. In 19 open-chest dogs, the left anterior descending coronary artery was occluded for 3h and then reperfused. Non-radioactive colored microspheres were injected into the left atrium to measure regional myocardial blood flow (RMBF). Immediately after occlusion, RMBF was reduced to 23 +/- 2% (of control) in the inner layer and 32 +/- 2% in the outer layer. Five minutes after reperfusion, RMBF was increased to 170 +/- 20% and 156 +/- 11% of control in the inner and outer layers, respectively. One week later, RMBF in the inner layer was reduced to 63 +/- 4% but it was not reduced (100 +/- 6%) in the outer layer. There was a roughly positive correlation between the inner/outer flow ratio measured 5 min after reperfusion and myocardial creatine kinase activity. Myocardial necrosis determined by triphenyl tetrazolium chloride stain varied inversely with the inner/outer flow ratio. These results indicate that good reflow in the inner layer 5 min after reperfusion is a favorable indicator for myocardial salvage.