Background Although it has been well known that patient with acute myocardial infarction (AMI) accompanied by acute heart failure (AHF) had poor clinical outcome, there are few available data in impact of AHF on in-hospital mortality in AMI patients after successful revascularization. Methods and Results To compare in-hospital mortality between AMI patients without and with AHF (Killip class II or III), we analyzed 9,158 AMI patients without cardiogenic shock or Killip class IV at admission underwent successful percutaneous coronary intervention from Korea Acute Myocardial Infarction Registry (KAMIR) between Oct. 2005 and Jan. 2008. Of these, 1,838 patients (20.1%) had diagnosis of AHF at admission. Patients with AHF were older (65.68 짹 12.07 vs. 61.06 짹 12.28) and were more common in female gender (34.3% vs. 25.1%), history of hypertension (52.2% vs. 46.9%), diabetes (32.3% vs. 24.7%), ischemic heart disease (15.5% vs. 12.4%) and left main or 3 vessel disease (30.4% vs. 23.7%) than those without AHF (p<0.001 respectively). Patients with AHF had also lower cleatinine clearance and ejection fraction than those without AHF (62.39 짹 34.78 vs. 74.20 짹 36.41; 47.63 짹 15.76 vs. 53.71 짹 17.74, p<0.001 respectively). However, patients without AHF were more common in history of smoking and family history of coronary artery disease (38.3% vs. 47.3%; 4.8 vs. 7.4%, p<0.001 respectively). Patient with AHF had significantly higher incidence of in-hospital mortality than those without AHF (5.6% vs. 1.2%, p<0.001). By multivariate logistic regression, the independent predictors for in-hospital mortality were age, creatinine clearance, ejection fraction and presented with AHF [odds ratio (OR)=1.043; 95% Confidence interval (CI)=1.017-1.070, OR=0.969; 95% CI=0.958-0.981, OR=0.924; 95% CI=0.908-0.941, and OR=2.413; 95% CI=1.555-3.744]. In subgroup analyses, AHF was the independent predictor in old ages, male gender, patients with chronic kidney disease (CKD) and ST segment elevation MI (OR=2.430; 95% CI=1.493-3.955, OR=2.965; 95% CI=1.685-5.219, OR=2.619; 95% CI=1.607-4.268 and OR=2.862, 95% CI=1.689-4.851). Conclusions Despite of successful revascularization, AHF is still associated with in-hospital mortality in AMI patient. Therefore, intensive and meticulous management should be needed for AMI patients with AHF, especially in old ages, male gender, with CKD and ST elevation MI.