Background: Bifurcated coronary lesion is common complex lesions in daily practive and various techniques are being used for it. Myocardial necrosis can occur during PCI, and it is suggested to be aggravated in bifurcated lesion. We tried to investigate the mechanisms of periprocedural infarction using IVUS and delayed-enhancement MRI. Methods: Thirty-three patients who underwent elective bifurcation PCI were enrolled. Bifurcation PCI was attempted by single stent with final kissing technique at first. If significant residual stenosis (> 50%) or type C dissection or decreased flow developed at side branch, provisional second stent was deployed using T-stenting and small protrusion technique (TAP-stenting). The amount of distal embolization of plaque material was measured in all main and side vessel by IVUS 3D volumetric analysis. Myocardial damage was evaluated by CK-MB and the volume of gadolinium hyperenhancement. Results: There was no case of loss or decreased flow of side branch in both two stents (N=13) and one stent (N=18) group. IVUS-measured pre-procedural plaque volume of treated segment of main vessel was not different between two groups (182.01짹75.52 mm3 versus 185.1짹66.61, p=NS). Two stent group showed significantly higher plaque volume in side branch (50.67짹37.52 versus 21.70짹14.65, p=0.014) and higher post-procedural CK-MB (13.95짹4.98 versus 3.08짹3.38 ng/mL, p=0.017) than one stent group. However, the frequency of MRI hyperenhancement (5 (38.4%) of two stent group and 7 (38.9%) of one stent group) or the volume of hyperenhanced segment was not significantly different between two groups. Also, the correlation between changes in plaque volume of both branches, CK-MB, and MRI hyperenhancement volume was marginal (p=NS). Conclusion: Our data suggest that distal embolization of plaque is not uncommon in PCI, and PCI of bifurcated lesion with high plaque volume at side branch might drive the need of provisional second stent and lead to higher myocardial damage. Because periprocedural myocardial damage is known to be related to cardiovascular prognosis, efforts to minimize myocardial damage should be considered in bifurcation PCI.