Background: Eccentric and ruptured plaque with or without thrombi observed by intravascular ultrasonography (IVUS) was reported to be associated with postprocedural myocardial infarction. However, in the absence of these typical morphologic features, it is difficult to predict postprocedural myocardial damage based on IVUS findings. The purpose of our study is to evaluate the association of coronary plaque composition characterized by IB-IVUS system (YD Ltd, Japan) with postprocedural myocardial infarction. Methods: One hundred eleven significant de novo coronary lesions were evaluated with a 30 MHz phased-array IVUS catheter with motorized pull-back system at 0.5 mm/s (Galaxy II, Boston Scientific, USA) prior to percutaneous coronary intervention (PCI) with stenting. Tissue characterization of target lesions by IB-IVUS was based on radiofrequency backscatter signal analysis. Radiofrequency signals were classified into four component types: calcification, fibrotic tissue, mixed tissue, and lipid pool. For each cross section image, the content of these plaque components was assessed by an integrated soft ware. Total and mean content values for each tissue component from all the image slices for each lesion were obtained. Lesions were divided into two groups according to CK-MB elevation after PCI : group I (n=37) with CK-MB elevation ��� 3 times upper normal limits and group II (n=84) with less CK-MB level elevation than group I. CTO, bifurcated or heavily calcified coronary lesions were excluded. Results: Baseline characteristics including risk factors, laboratory findings including lipid profile, angiographic QCA and conventional IVUS parameters such as plaque area and lumen area showed no significant difference between the two groups. However, group I showed a significantly larger mean content of scattered calcium compared to group II (2.7짹 3.2% vs. 1.5짹 1.4%, p=0.033). Lipid pool content was similar between the two groups. Conclusions: A large content of scattered tissue calcification in target lesions analyzed by IB-IVUS seems to be associated with post-PCI myocardial infarction. However, mere calculation of lipid pool amount by IB-IVUS could not predict the risk of postprocedural myocardial infarction.