BACKGROUND Epicardial coronary flow is occasionally reduced even after coronary intervention despite the absence of vessel obstruction in patients with acute myocardial infarction. Our aim was to clarify the cause and outcomes of radiocontrast slow filling in patients with reperfused acute anterior myocardial infarction by assessing microvascular damage with the use of myocardial contrast echocardiography (MCE) and functional outcomes. RESULTS We carefully reviewed the cineangiograms of 86 patients who achieved coronary revascularization within 12 hours of the onset and underwent MCE before and soon after recanalization with the intracoronary injection of sonicated microbubbles. Antegrade coronary flow after recanalization was graded by two observers based on Thrombolysis in Myocardial Infarction (TIMI) trial flow grades. Left ventricular ejection fraction was measured on the day of infarction and 1 month later. TIMI grade 2 was observed in 18 patients (21%), and the other 68 patients manifested TIMI grade 3 after recanalization. All patients with TIMI 2 showed substantial MCE no reflow, whereas only 11 patients (16%) with TIMI 3 showed MCE no reflow. Functional improvement was worse in patients with TIMI 2 than in those with TIMI 3 (TIMI 2, 38 +/- 8% versus 40 +/- 8%, P = NS [acute versus late]; TIMI 3, 44 +/- 13% versus 55 +/- 13%, P < .001). Among patients with TIMI 3, significant functional improvement was observed only in patients with MCE reflow (MCE reflow, 46 +/- 13% versus 57 +/- 12%, P < .001; MCE no reflow, 35 +/- 11% versus 45 +/- 12%, P = NS). CONCLUSIONS Despite no obstructive lesion of the vessel, TIMI 2 is caused by advanced microvascular damage and is a highly specific, although not sensitive, predictor of poor functional outcomes in patients with acute myocardial infarction. TIMI 3 does not necessarily indicate myocardial salvage, and detection of MCE no reflow in these patients is particularly useful for the prediction of functional outcome.