Coronary flow reserve is not fully restored immediately after revascularization of an occluded vessel. The present study examined the coronary flow impairment in patients with acute myocardial infarction (AMI) after successful balloon angioplasty or spontaneous recanalization (without residual epicardial coronary stenosis). Fourteen patients underwent thallium-201 dipyridamole scintigraphy in the acute phase (mean 5.9 days) and in the chronic phase (mean 24. 6 days) after AMI. A 201Tl reinjection study was carried out only in the acute phase of AMI. The fill-in phenomenon was assessed by the %201Tl uptake in the infarct region after 201Tl reinjection, and positive (n=8) and negative (n=6) fill-in groups were distinguished. The %201Tl uptake increased from the acute phase study to the chronic phase study in the positive fill-in group (56.1%+/-4.1% to 74.4%+/-13.6%, P<0.001), whereas it decreased in the negative fill-in group (54.0%+/-10.6% to 43.7%+/-9.9%, P<0.05). The change in %201Tl uptake following reinjection was significantly correlated with the improvement in regional ventricular wall motion in the chronic phase (r=0.85, P<0.001). We conclude that the impaired coronary flow reserve persisted after balloon angioplasty or spontaneous recanalization, which might indicate the presence of "microvascular stunning". The increase in %201Tl uptake predicted the change in ventricular wall motion.