Background: Patients (pts) with non-ST elevation myocardial infarction (NSTEMI) are increasingly being treated with early percutaneous coronary intervention (PCI). However, the efficacy and safety of PCI in NSTEMI pts with advanced heart failure (Killip class 3 or 4) are largely unknown. Methods: A total 483 pts who presented with NSTEMI with advanced heart failure (Killip class 3 or 4) enrolled in the Korea Acute Myocardial Infarction Registry (KAMIR) from Jan 2005 to Dec 2006 were analysed. In-hospital and 6-month clinical outcomes of early invasive strategy (Early PCI group, n = 236) were compared with those of medical treatment (Conservative group, n = 147). Results: The pts with early PCI group showed younger age (69.61 짹 10.57 vs 72.14 짹 11.74, P=0.030), lower body mass index (BMI, 23.42 짹 3.18 vs 22.69 짹 3.36, P=0.043), and lower heart rate (87.67 짹 25.19 vs 93.63 짹 29.14, P=0.036) compared with those of conservative group. Stents were implanted in 157 (66.3%) pts in early PCI group, and drug-eluting stents were used in 147 (93%) among them. Procedural success rate was 97.2%. In-hospital mortality was significant higher in the conservative group (19.7% vs 8.5%, P=0.001). At 6-month follow up, the incidence of all cause mortality was remained higher in the conservative group (12.9% vs 5.9%, P=0.018), but the survival and freedom from major adverse cardiac events (MACE)s was similar between the two groups (10.2% vs 13.6%, P=0.305) possibly because of the trend toward higher incidence of coronary artery bypass graft (CABG) in the early PCI group (3.4% vs 0.7%, P=0.089). Conclusion: Early invasive strategy in NSTEMI patients with advanced heart failure significantly decreased in-hospital and mid-term mortality without obvious complications, However, increased surgical revascularization rate in the early PCI group resulted in similar survival and freedom from MACE in both groups.