Objectives and Methods: We used intravascular ultrasound (IVUS) to assess the incidence, predictors, and outcome of plaque prolapse (PP) after stent implantation (138 Sirolimus-eluting stent; 49 Paclitaxel-eluting stent; 123 Bare-metal stents) in 310 acute myocardial infarction (AMI) patients. PP was defined as tissue extrusion through the stent strut post-procedure. Results: After stenting, PP was detected in 27.4% (maximum PP area; 0.7짹0.5 mm2, PP volume; 2.3짹1.7 mm3). In patients with PP, stent length was longer (30.9짹13.4 vs. 21.5짹8.5 mm, p<0.001); more stents were deployed (1.5짹0.6 vs. 1.1짹0.3, p<0.001); and inflation pressure was significantly higher (15.3짹2.9 vs. 14.1짹2.6 mmHg, p=0.001). Lesion site plaque burden was greater; calcium arc was smaller; the presence of positive remodeling, hypoechoic plaque, plaque rupture, and thrombus were significantly more common in patients with PP. Cardiac enzyme was more significantly elevated after stenting in patients with PP (Table). Multivariate analysis showed that stent length (HR=2.39; 95% CI 1.17-3.89, p=0.003), plaque rupture (HR=1.96; 95% CI 1.14-3.37, p=0.015), and positive remodeling (HR=1.72; 95% CI 1.01-2.92, p=0.044) were independently associated with the development of PP. Conclusions: Pre-intervention IVUS lesion characteristics – plaque rupture and positive remodeling – and longer stent length predict PP, and PP is associated with myonecrosis after stenting for infarct-related artery in patients with AMI.