ST elevation myocardial infarction Left main stenosis, totally occluded lesion Angiographically visible thrombus, significant lesion within the main branch proximal to the stented segment, significant distal lesion at a side branch Regional wall motion abnormalities of the stented artery and jailed side branch segments Left ventricular ejection fraction<40% Primary myocardial disease Serum creatinine >2mg/dl Predilatation of side branch before the main branch stent implantation Contraindications to adenosine