Oral health problems are common and are associated with various geriatric conditions in older adults. The importance of oral health has not been fully highlighted in the assessment and management of patients with heart failure. Here, we investigated the clinical implications of oral assessment in elderly patients with acute heart failure. We evaluated oral health using the revised oral assessment guide in 77 patients aged 65 years or older who were admitted to hospital for acute heart failure. Poor oral health (defined as a revised oral assessment guide score ≥ 9) was identified in 66.2% of the patients. Patients with poor oral health had high prevalence of decreased physical function, undernutrition, and cognitive impairment. A reduction in the Barthel Index, as an indicator of activities of daily living during hospitalization, was significant in the enrolled patients. The Barthel Index decreased more in patients with poor oral health than those with normal oral health. Furthermore, the revised oral assessment guide score on admission was found to be the only independent predictor of changes in the Barthel Index during hospitalization in the multivariate regression analyses. In conclusion, oral assessment using the revised oral assessment guide during hospitalization could provide useful information for the management of elderly heart failure patients.