Methods and Results:Using a HF database that collates DPC data and electronic medical records from 3 hospitals in Japan, we investigated factors contributing to prolonged hospitalization and in-hospital death, based on clinical characteristics and data obtained early during hospitalization in 2,750 Japanese patients with HF hospitalized between 2011 and 2015. Mean age was 77.0±13.0 years; 55.3% (n=1,520) were men, and 39.1% (n=759) had left ventricular ejection fraction <40%. In-hospital mortality was 6.0% (n=164) and mean length of stay for patients who were discharged alive was 18.2±13.7 days (median, 15 days). Factors contributing to in-hospital death were advanced age, higher New York Heart Association (NYHA) class, low albumin and sodium, and high creatinine and C-reactive protein (CRP). Factors contributing to prolonged hospitalization were higher NYHA class, low Barthel index, low albumin, and high B-type natriuretic peptide, lactate dehydrogenase, and CRP.