['The Killip classification categorizes heart failure (HF) in acute myocardial infarction, and has a prognostic value. Although non-ST-elevation myocardial infarction (NSTEMI) is increasing steadily, little information is available about the prognostic value of low Killip class in this scenario. Our aim was to assess the prognostic value of mild HF in NSTEMI.', '835 patients with NSTEMI between 2005 and 2007 were prospectively recruited. Patients in Killip-1 (K1=684) or Killip-2 class (K2=113) were selected (38, with K>2, excluded). Clinical, angiographic, treatment strategies, and 30-day all-cause mortality, together with other cardiovascular outcomes were recorded.', 'K2 patients were mostly women (K1 27.9% vs K2 48.0%, p<0.001) and older (K1 66.6years vs K2 73.8years, p<0.001) with a higher frequency of diabetes mellitus (p<0.001) and hypertension (p<0.001). Smoking was less frequent in the K2-group (p=0.003). A previous infarction/revascularization history was similar in both groups. The infarction size, assessed by Troponin I/Creatin kinase, did not differ between groups (p=0.378 and p=0.855). Multivessel coronary disease and revascularization procedures were less common in group K2 (p=0.015 and p=0.005 vs group K1, respectively). Patients in K2 had a worse prognosis in terms of maximum Killip class, death and major adverse cardiovascular events (p<0.001). After multivariate analysis, mild HF at presentation was an independent risk factor for mortality (OR=6.50; IC 95%: 2.48-16.95; p<0.001).'] Is mild heart failure a mortality marker after a non-ST-segment acute myocardial infarction?