To treat patients with acute myocardial infarction, primary percutaneous coronary intervention (PCI) will be performed with the use of an everolimus-eluting cobalt- chromium stent (everolimus-eluting stent: EES, Xience Prime, Xpedition), which is the current standard drug-eluting stent (DES). Vascular responses at the site of stent placement will be evaluated by optical coherence tomography (OCT) at 2 weeks or 3 months and at 12 months after stent placement, along with observation of changes over time in the target vessel. The relationships between OCT findings and the time course of platelet aggregation and between OCT findings and the occurrence of major cardio- cerebrovascular events will also be elucidated.