Self-care is a cornerstone for the successful management of heart failure (HF). The purpose of this study was to examine the impacts of HF self-care on prognosis in Japanese patients with HF. A total of 283 HF outpatients (age 64 ± 14, 70% male, 52% HFrEF) were enrolled. We asked patients to answer about their adhevence to 5 self-care behaviors (medication, eating a low-sodium diet, regular exercise, daily weight check, and treatment seeking behavior). On the basis of the results, we classified patients into a good self-care group and a poor self-care group. The primary outcome was HF hospitalization and/or cardiac death. In total, 65% of patients were classified into the poor self-care group. During a median follow-up of 2 years, cardiac events occurred more frequently in the poor self-care group (22% versus 9.6%, P = 0.013). Poor self-care was an independent risk factor for cardiac events in Cox regression analysis adjusted for clinical parameters (hazard ratio = 2.86, P = 0.005). Poor self-care was also associated with an increased number of HF hospitalizations as well as an extended length of hospital stay for HF. Poor knowledge about HF was an independent determinant for poor self-care in multivariate logistic regression analysis (odds ratio = 0.92, P = 0.019). Insufficient self-care is an independent risk factor for cardiac events in Japanese patients with HF.