Aim: To determine the impact of self-efficacy-based training on the adherence to treatment among patients diagnosed with heart failure. Material and methods: After obtaining ethical permission from the Ethics Committee, we conducted quasi-experimental research including 100 heart failure patients who were hospitalized to the coronary care and cardiac critical care units. The sample size was determined to be 50 persons each group, resulting in a total of 100 participants. The study included individuals who met the following criteria: a confirmed diagnosis of heart failure by a physician, at least 24 hours after admission, aged between 30 and 62 years, without any speech, hearing, or visual impairments, possessing basic literacy skills, having an ejection fraction (EF) of 15 to 40% as determined by ECG results, no previous history of mental disorders, and neither the patient nor any family members being employed in the medical profession. Results: Prior to the intervention, the average treatment adherence scores in the intervention and control groups were 50.95 ± 10.33 and 48.76 ± 8.64, respectively. Following the intervention, these scores increased to 71.58 ± 9.95 and 50.06 ± 9.42. The paired samples t-test revealed a statistically significant rise in treatment adherence scores among patients in the intervention group after the intervention, as compared to before the intervention (P = 0.001). Conversely, the control group did not experience a significant change in treatment adherence scores before and after the intervention (P = 0.43). Furthermore, the independent samples t-test revealed substantial disparities in the average treatment adherence ratings between the two groups after the intervention (P = 0.001). Conclusions: The findings of this research suggest that a training program focused on self-efficacy may greatly improve medication adherence in individuals with heart failure. Hence, the creation and execution of self-efficacy-focused training programs, which are economical and promote involvement from individuals with heart failure, may result in enhancements in patient outcomes.