Background: Heart failure (HF) is a leading cause of morbidity and mortality in developed countries. Also in Korea, acute decompensated heart failure (ADHF) becomes more prevalent and require large amount of public health resources. But very little information is available on the clinical characteristics and prognosis of patients with ADHF in Korea, especially on the patients with severe LV dysfunction. Methods: The KorHF Registry Database composed of 3,200 patients, which enrolled hospitalized patients with ADHF from 28 university hospitals in Korea from Nov, 2005 to Nov. 2009. According to LV End diastolic dimension (EDD) and LV ejection fraction(EF) on echocardiogram, the patients with LV dysfunction are classified to Mild, Moderate and Severe LV dysfunction groups. Severe LV dysfunction is defined by EDD���63 and EF���27 which are representative values of 25 percentile in distribution curve of EDD, EF respectively. Results: The total of 388 patients show severe LV dysfunction and 220 patients moderate, 216 patients mild degree respectively. The mean age of severe LV dysfunction is 60.3짹15 years, which is lower than those of other groups (69.0, 67.1 yrs respectively, p<0.01), and severe LV dysfunction is shown more frequently in men(68.2% vs 43%, 58.6%, p<0.01). Patients with severe LV dysfunction have more frequent history of previous HF(42.9% vs 20.3%, 31% respectively, p<0.01), less frequent history of hypertension(31.9% vs 48.6%, 53.6% p<0.01), DM(20.1% vs 37.5%, 36.8%, p<0.01) and ischemic heart disease(24.3% vs 49.7%, 45.0%, p<0.01). Severe LV dysfunction group show lower systolic blood pressure(122mmHg vs 133mmHg. P<0.01) at admission. But there are no differences in DBP, HR, BNP, BUN/Cr, Na level at admission. Expected event free survival rate (death or readmission) of severe LV dysfunction group at 1, 2 and 3 year are 0.670, 0.558 and 0.469 respectively, which are not inferior to those of mild or moderate groups.Event free survival rates according to EDD or EF show no significance, but show significant difference according to NYHA class Conclusion: Data from Korean acute heart failure registry provided important insights into the clinical characteristics, clinical outcome of severe LV dysfunction patients. Even on the patients who show severe LV dysfunction at admission, optimal medical therapy is needed and expected to bring non-inferior outcome compared to the patients with mild or moderate LV dysfunction.