Objectives:We conducted an analysis of first-time tolvaptan users (≥80 years old) to determine the factors associated with the prognosis of elderly patients with heart failure.Methods:We retrospectively analyzed 66 consecutive patients with worsening heart failure (aged ≥80 years) who were admitted to Fujita Health University Bantane Hospital from 2011 to 2016 and treated with tolvaptan. Differences between the in-hospital death and survival groups were evaluated. Multivariate logistic regression analysis was also performed to identify the risk factors for mortality.Results:Sixty-six patients were included, and 26 patients died during the index hospitalization. The patients who died had a significantly higher prevalence of ischemic heart disease; a higher heart rate; higher levels of plasma C-reactive protein, blood urea nitrogen (BUN), and creatinine; a lower serum albumin level; and a lower estimated glomerular filtration rate than surviving patients. The proportion of patients requiring early initiation of tolvaptan treatment (within 3 days of admission) was significantly higher in surviving patients. On the basis of multivariate logistic regression analysis, although a high heart rate and high BUN levels were independent factors for in-hospital prognosis, they were not significantly associated with the early use of tolvaptan (≤3 days vs. ≥4 days; odds ratio=0.39; 95% confidence interval=0.07–2.21; p=0.29).Conclusions:This study revealed that a higher heart rate and higher BUN levels were independent factors for in-hospital prognosis in elderly patients who received tolvaptan and that early tolvaptan use may not always be effective in elderly patients.