Circulation Journal Official Journal of the Japanese Circulation Society http://www. j-circ.or.jp rimary percutaneous coronary intervention (PCI) is now established as a first-line therapeutic strategy for patients with acute myocardial infarction (AMI), and accumulating evidence has shown that primary PCI can improve the prognosis in AMI patients suffering from cardiogenic shock. 1-4 In addition to the interventional treatment, mechanical assist devices such as intra-aortic balloon pumping (IABP) and percutaneous cardiopulmonary support (PCPS) are indispensable for AMI patients complicated with cardiogenic shock, refractory malignant arrhythmia, advanced heart failure, or failed reperfusion. Thus, the AMI patients requiring mechanical support devices are considered as a subgroup of high-risk AMI patients with high in-hospital morbidity and mortality. Recently, we have already demonstrated that repeat-AMI patients undergoing primary PCI, a subgroup of high-risk patients with AMI had a significantly higher in-hospital mortality rate than first-AMI patients, and determinants of in-hospital outcome in recurrent-AMI patients undergoing primary PCI were different from those in first-AMI patients. Background: Predictors of in-hospital outcome after primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) requiring mechanical support devices such as intra-aortic balloon pumping (IABP) and/or percutaneous cardiopulmonary support (PCPS) remain unclear.