Introduction: There has been controversy that total revascularization in patients with acute myocardial infarction (AMI) has efficacy in preventing heart failure. Hypothesis: We investigated the clinical outcomes of incomplete revascularization in patients with AMI who had remnant critical coronary stenosis. Methods: A total of 1,899 patients with AMI who had not heart failure and underwent percutaneous coronary intervention (PCI) in a nationwide prospective Korea AMI Registry (KAMIR) from November 2005 to January 2008 were divided into two groups by a presence of remnant critical coronary stenosis (���70% diameter stenosis in three epicardial arteries). Group I had one or more remnant lesions (n=696, 73.1% male, 62.4짹11.6 years) and group II did not have any remnant lesions (n=1203, 77.2% male, 59.1짹11.8 years). All patients were evaluated by baseline and follow-up 2-dimensional echocardiography to determine ejection fraction (EF) during follow-up periods (mean 207.6짹81.9 days). End-points were new symptomatic heart failure (NYHA class ���2) with EF less than 40%, death or re-MI, and re-PCI during one-year clinical follow-up. Results: Group I had more atherosclerotic risk factors and showed higher admission creatinine level (���1.3 mg/dL). During PCI, drug-eluting stents were more implanted in group I (94.3% vs. 91.5%, p = 0.029) and more peri-procedural cardiogenic shock was developed in group I. End-points occurred in 327 patients (17.3%) during one-year follow-up. In multi-variate analysis, remnant coronary lesion was an independent predictor of new heart failure (hazard ratio [HR] 1.68, 95% confidence interval [CI] 1.03 to 2.82, p = 0.037) and re-PCI (HR 1.94, 95% CI 1.47 to 2.57, p <0.001). However, it did not predict death or MI (HR 1.64, 95% CI 0.83 to 3.24, p = 0.157). Although baseline EF was lower in group I (54.9짹8.9% vs. 55.9짹9.5%, p = 0.025), there was no difference of EF in follow-up echocardiography. Independent predictors associated with development of new heart failure were presence of persistent coronary stenosis, age ��� 65 years, left anterior descending artery as a culprit vessel, and lower baseline EF. Conclusion: We should consider more aggressive revascularization strategy in patients with AMI to prevent development of new heart failure.