Background The possibility that stem cell might aggravate atherosclerosis or restenosis has been regarded as a potential limitation of stem cell therapy in myocardial infarction. In this study, we evaluated the changes of coronary artery with intravascular ultrasound (IVUS) in patients enrolled in MAGIC Cell-3-DES trial. Methods and Results Among 50 patients with acute myocardial infarction who underwent coronary revascularization with either sirolimus-eluting stents (SES) or paclitaxel-eluting stents (PES) implantation for the culprit lesion, we analyzed IVUS in 33 patients (control group : n=17 and cell infusion group : n=20). In the cell infusion group, peripheral blood stem cells mobilized by G-CSF were delivered via intracoronary infusion into infarcted myocardium. We evaluated proximal and distal reference segments, and stented segments at immediate post-intervention and 6 month follow-up respectively. In the proximal and distal reference segments, the serial changes of lumen area (LA), vessel area (VA), and plaque plus media area (PMA) were not significantly different between the cell infusion and the control groups. Mean neointimal area (NIA) in stented segments was similar between the two groups. (cell infusion: 0.2짹0.4 mm짼 vs. control: 0.3짹0.4 mm짼, p>0.05). However, there was a significant increase in mean peri-stent area (PSA) in the cell infusion group compared to the control group (0.7짹1.4 mm짼 vs. -0.1짹1.2 mm짼, p<0.05). This difference mainly comes from PES implanted group (1.9짹1.2 mm짼 vs. 0.2짹0.6 mm짼, p<0.01) rather than SES implanted group (0.1짹1.0 mm짼 vs. -0.1짹1.5 mm짼, p>0.05). Conclusions Intra-coronary stem cell infusion after DES implantation does not aggravate neointimal hyperplasia. However, it may induce peri-stent positive remodeling especially in patients receiving PES, but not in non-stented segments. To evaluate the effect of stem cell therapy on coronary vasculature, longer term follow-up is needed.