Background: Enhancing treatment adherence is a crucial component of heart failure management. Training intervention programs focused on self-efficacy can play a significant role in improving treatment adherence, thereby reducing hospital readmissions and treatment costs for patients with heart failure. Objectives: This study aimed to assess the impact of a self-efficacy-based training intervention program on treatment adherence among patients with heart failure admitted to teaching hospitals affiliated with Zahedan University of Medical Sciences. Methods: This quasi-experimental study included 70 patients with heart failure admitted to the coronary care and cardiac intensive care units of Khatam Al-Anbia (PBUH) and Ali Ibne Abi Talib (PBUH) hospitals in 2021. Participants were selected through convenience sampling based on inclusion criteria and were randomly assigned to intervention and control groups using colored cards. Both groups filled out a demographic information questionnaire and the Treatment Adherence Scale at the beginning of the study. The intervention group participated in a self-efficacy-based training program for 45 minutes daily over four consecutive days. This program's content was reinforced through weekly phone calls to the intervention group patients for three months post-intervention. Conversely, the control group received standard ward education. The Treatment Adherence Scale was administered again to both groups three months after the intervention. Results: An independent samples t-test revealed no significant difference in mean treatment adherence scores between the intervention and control groups before the intervention (P = 0.28). However, there was a significant difference in mean treatment adherence scores post-intervention (P = 0.001). Conclusions: The self-efficacy-based training intervention program effectively improved treatment adherence among patients with heart failure. Therefore, developing and implementing such training interventions could significantly enhance treatment adherence at a minimal cost while maximizing patient participation.