We evaluated the in-hospital and 1-year outcomes and predictors of admission heart failure in patients with non-ST-elevation acute coronary syndromes (NSTE-ACSs) without previous heart failure. We analyzed 4,825 patients with NSTE-ACS without a history of congestive heart failure who were included in the multicenter Canadian ACS Registries. Patients in Killip's class II/III on admission (n = 559, 11.6%) were compared with patients in Killip's class I. Patients with heart failure on admission were older (72 [64, 79] vs 64 [54, 73] years, p < 0.0001), with higher baseline creatinine levels (96 vs 88 mmol/dl, p <0.0001), more diabetes (32.2% vs 22.8%, p < 0.0001), hypertension (58% vs 52.4%, p = 0.014), previous myocardial infarction (MI; 38.9% vs 30.3%, p < 0.0001), previous stroke (13.5% vs 7.4%, p < 0.0001), and had more ST depression on admission (27.7% vs 17.3%, p < 0.0001). In-hospital treatment was similar except for a lower rate of aspirin therapy and fewer coronary interventions. Crude event rates were significantly higher in patients with heart failure (in-hospital death 3.6% vs 1.1%, p < 0.0001; death or MI 7.9% vs 4.7%, p = 0.0011; stroke 1.1% vs 0.4%, p = 0.03). One-year event rates were also higher in patients with heart failure (death 14.6% vs 4.4%, p < 0.0001; MI 9.3% vs 6.6%, p = 0.03; death or MI 21.5% vs 10.3%, p < 0.0001). Variables independently associated with heart failure were age (odds ratio 1.57, 95% confidence interval 1.43 to 1.73), diabetes mellitus (odds ratio 1.53, 95% confidence interval 1.24 to 1.89), admission ST depression (odds ratio 1.52, 95% confidence interval 1.22 to 1.90), previous MI, and baseline creatinine. Heart failure on admission was an independent predictor of in-hospital death, death or MI, and stroke and of 1-year death and death or MI. In conclusion, in patients with NSTE-ACS, heart failure on admission is associated with increased short- and long-term rates of death and MI.