Background: The oral vasopressin-2 receptor antagonist, tolvaptan, causes aquaresis and improves symptoms in patients with congestive heart failure. However, few studies have explored the effect of tolvaptan in acute heart failure (AHF) patients ≥90 years old. Methods: This study enrolled 106 AHF patients treated with tolvaptan added to standard therapy. The subjects were divided into 2 groups: ≥90-year-old patients (over-90 group, mean 92 ± 2 years, n = 45) and <90-year-old patients (under-90 group, mean 76 ± 11 years, n = 61). Patients’ characteristics were assessed, and efficacy and safety were compared between the 2 groups. Results: The over-90 group had a lower proportion of male patients, lower body weight, and higher ejection fraction. The under-90 group had significantly higher prevalence of ischemic heart disease and diabetes mellitus. There were no significant differences between the 2 groups in total urine volume at 24 and 48 hours (1934 ± 983 mL vs 1816 ± 1028 mL, P = 0.58 and 3806 ± 1444 mL vs 4078 ± 1851 mL, P=0.47, respectively), the mean change in body weight (−3.0 ± 2.7 kg vs −2.6 ± 2.6 kg, P = 0.50), improvement of congestive symptoms, changes in serum sodium and creatinine levels, the incidences of hypernatremia (n = 0, 0% vs n = 1, 1.6%, P = 0.63), and worsening renal function (n = 9, 20% vs n = 17, 28%, P = 0.48). Conclusion: The efficacy and safety of tolvaptan in AHF patients aged more than 90 years were comparable to those of <90 years old. Tolvaptan provides a complementary therapeutic option for AHF patients aged more than 90 years.