Coronary flow velocity pattern in patients with acute myocardial infarction demonstrating no-reflow phenomenon is characterized with early systolic retrograde flow and rapid deceleration of diastolic flow velocity. In this study, we investigated the early temporal changes in microvascular function in patients with the no-reflow phenomenon. Among 144 patients with a first acute myocardial infarction, 33 exhibited sizable no-reflow phenomenon after coronary reperfusion with myocardial contrast echocardiography. We assessed temporal changes in coronary flow velocity patterns with the Doppler guidewire. The early systolic retrograde flow was observed < or = 10 seconds after reperfusion in 16 patients (group A) or later in 17 patients (331 +/- 327 seconds, group B). Diastolic deceleration rate was higher in group A than in group B at 1 minute after reperfusion. It gradually increased in group B and showed comparable value to group A 10 minutes later. Group A had longer elapsed time from symptom onset to reperfusion and a greater number of infarct Q waves before reperfusion than group B (14 +/- 13 vs 5 +/- 2 hours, p <0.01; and 3 +/- 2 vs 2 +/- 1, p <0.02). In contrast, the incidence of transient ST reelevation shortly after reperfusion was higher in group B (76% vs 25%, p <0.01). Thus, the characteristic coronary flow velocity pattern is either established at the moment of coronary reperfusion or progresses thereafter in patients with no-reflow phenomenon. This suggests different mechanisms of developing ischemic microvascular injury.