Aim To investigate the predictive factors of cardiac events including rehospitalization for worsening heart failure (HF) and cardiac death within 1 year after hospital discharge in octogenarians hospitalized for HF. Methods We retrospectively analyzed in detail clinical data for patients aged >80 years who were admitted to Kochi University, Kochi, Japan, for acute decompensated HF in order to identify predictive factors for cardiac events within 1 year. Results A total of 67 patients (mean age of 85 ± 4 years, 39 men) were included, and 28 patients (41.8%) had cardiac events. The patients with cardiac events were significantly older, had a lower prescription rate of beta‐blockers at discharge and had a lower rate of arrhythmia as an exacerbating factor of HF than patients without cardiac events. When nutritional status was assessed by the controlling nutritional status (CONUT) score, patients in the cardiac events group had significant malnutrition (CONUT ≥5). In addition, Kaplan–Meier analysis showed that patients with CONUT ≥5 had a higher incidence of cardiac events than did those with a CONUT <5 (log–rank, P < 0.038). In logistic analysis, the independent determinants of the cardiac events within 1 year were malnutrition at moderate or severe levels by the CONUT score and no beta‐blocker medication. Conclusions In very elderly patients hospitalized for HF, malnutrition and no beta‐blocker medication were predictors of rehospitalization for worsening HF or cardiac death within 1 year. These factors could be meaningful targets for improving the management of octogenarians with HF. Geriatr Gerontol Int 2017; ••: ••–••.