A thin myocardial layer adjacent to the epicardium (epicardial rim) often survives after transmural myocardial infarction. Regional myocardial blood flow (Qm) at this rim may be high enough to maintain myocardial viability during coronary occlusion. To test this hypothesis, we measured Qm in 12 anesthetized dogs during left anterior descending coronary artery occlusion using nonradioactive colored microspheres. Myocardium in the region supplied by the occluded artery was sliced into sections approximately 0.5 mm thick from the epicardial surface to the endocardium, and the Qm in each section was determined. During occlusion, the Qm of myocardium within 0.5 mm of the epicardial surface remained at 74.8 +/- 8.8% of the preocclusion level. Maintenance of this high Qm during occlusion was abolished when an epicardial incision approximately 1 mm deep was made around the occluded area. These findings suggest that Qm is maintained at a surprisingly high level at the epicardial rim after coronary occlusion through epicardial arterial communications, which may be sufficient to maintain myocardial viability.