Background: Our previous study showed that intracoronary infusion of peripheral blood stem cells (PBSC) mobilized with G-CSF improved left ventricular (LV) function. But the parameters which could be predictors for myocardial recovery and changes in microvascular function after stem cell therapy is not well-known. Methods: From our prospective randomized stem cell therapy trial(total n = 62), 29 patients with acute myocardial infarction (Cell infusion group n=19, control group n=10), whose post-procedural and 6 month follow-up intracoronary Doppler study data and cardiac MRIs were available, are included in this study. There were no differences clinical and angiographic parameters between patients who were included in this study and those who were not. Coronary flow analysis was performed using Doppler wire (FlowWire, Cardiometrics) at 1.97짹1.56 days after myocardial infarction. The correlation of interval change in LVEF and intracoronary Doppler parameters (coronary flow reserve (CFR), deceleration time, average peak velocities and diastolic-to-systolic flow velocity ration (DSVR)) at the time of index procedure was analyzed. Results: Baseline clinical, angiographic and hemodynamic characteristics were not different between two groups. Ejection fraction (EF) changed from 51.1짹11.0 % to 58.2짹9.0% (p=0.001) in the cell infusion group. However, no change in LVEF was found in control group (53.1짹13.0 % vs. 54.4짹14.3 %, p=NS). CFR significantly increased in cell infusion group (1.64짹0.59 vs. 2.55짹0.72, p<0.001), but not in control group (1.74짹0.35 vs. 2.34짹0.37, p=NS). Percent change of CFR was much greater in cell infusion group ( 67.2짹64.6 % vs.23.4짹56.8 %, p<0.05). Baseline (r=0.57, p=0.002) and hyperemic (r=0.53, p=0.005) DSVRs showed a positive correlation with change of LV function. But, baseline CFR and other parameters had no correlation with LVEF improvement. Conclusion Intracoronary PBSC therapy resulted in better microvascular function recovery in patients with acute myocardial infarction. DSVR, but not baseline CFR itself correlated with recovery of LV function.