There is considerable clinical and experimental evidence of the benefit of late reperfusion of infarct-related arteries, referred to as the open artery hypothesis, in patients with acute myocardial infarction who presented too late to salvage at-risk ischemic myocardium. In addition to myocardial salvage, reperfusion of the infarct-related artery prevents infarct expansion, reduces development of ventricular remodeling, and decreases ventricular arrhythmia. The Occluded Artery Trial recently answered a major question related to the open artery hypothesis in a high-risk, asymptomatic patient with an occluded infarct artery. In this review, clinical and experimental evidence of the benefit of the open artery hypothesis will be discussed. (Korean Circulation J 2007;37:235-243)