Background and Objective: Cardiovascular disease is the most common cause of death and the major cause of disability in many countries, including Iran, and it causes stress and tension in afflicted patients. The aim of this study was to determine the effect of progressive muscle relaxation on perceived stress in patients with myocardial infarction. Materials and Methods: In this randomized clinical trial study, after sampling with a convenient method, the participants were randomly assigned to either the control or test group. The procedure included one orientation session for informing the participants with the study objectives and intervention method, followed by doing 120 intervention sessions for 2 months. Data collection tools included a demographic questionnaire, and perceived stress and self-reporting checklist. Results: A total of 66 patients participated in the study. The results of repeated measured ANOVA test on perceived stress show that there were no significant differences between the control and test groups pre-intervention. However, there was a significant difference between the two groups, 1 and 2 months post-intervention (P<0.001). Conclusion: Our findings show that performing the progressive muscle relaxation is an effective and useful technique for the treatment of perceived stress in patients with myocardial infarction. This technique is practically feasible, and it appears capable of decreasing the level of stress.