Background Patients with cardiovascular problems experience sleep disorders. Due to the importance of adequate sleep and rest for the growth and repair of damaged cells, it is necessary to use appropriate interventions to improve it.This study determined the effect of sleep intervention programs during cardiac rehabilitation on patients' sleep quality.Methods In this clinical trial study, 35 individuals participated in the cardiac rehabilitation program as the experimental group and 35 served as the control group. The program included 12 weeks of exercise, 3 sessions per week, and 3 sessions of training programs each lasting for 45 minutes, and a special two-session sleep improvement program. Data were collected using the Pittsburgh sleep quality index and analysed with descriptive and inferential statistical methods.ResultsThe two study groups were matched with age, sex, marital status, smoking and current disease diagnosis (P>0.05). The scores of sleep quality of patients were 9.2±1.58 before and 4.40±1.14 after intervention in the experimental group and 9.02±2.56 before and 7.48 ±1.86 after placebo in the control group. There was no significant difference before (P=0.73), but a significant difference after an intervention (P=0.0001). Also, scores of sleep quality of patients were significantly different in the experimental and control groups before and after the intervention (P=0.0001). Conclusion Findings indicated that the quality of sleep of cardiac patients improved after using the sleep intervention program during the cardiac rehabilitation program. Therefore, it is suggested to implement sleep improvement programs as an effective, easy, and feasible technique.