Background and Objective. 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. Materials and Methods. In this quasi-experimental study with unequal control group design, 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, 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. Results. There were not any significant differences between the two groups in age, sex, marital status, smoking, and indication for cardiac rehabilitation ( 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 intervention in the control group. There was no significant difference between the two groups before intervention ( P = 0.73 ). yet there was a significant difference after intervention ( P = 0.0001 ). In addition, scores of sleep quality of patients were significantly different in the experimental and control groups before and after intervention ( P = 0.0001 ). Conclusion. Findings indicated that the quality of sleep of cardiac patients improved after the sleep intervention program during the cardiac rehabilitation program. Therefore, it is suggested to implement sleep improvement programs for cardiac patient care as an effective, easy, and feasible technique. In addition, it is necessary to pay more attention to the sleep improvement program in cardiac rehabilitation. Trial Registration. The trial was retrospectively registered on https://en.irct.ir/trial/50799 on 14 September 2020 (14.09.2020) with registration number IRCT20140307016870N6.