Background <p>Cardiovascular diseases (CVDs) are a leading cause of death globally, yet patient participation in traditional cardiac rehabilitation programs is low. Home-based rehabilitation, especially when supported by technology, offers a promising alternative. This study aimed to determine the effectiveness of a home-based virtual exercise rehabilitation program, based on the Health Action Process Approach, for improving physical activity and psychological constructs in patients with myocardial infarction.</p> Methods <p>This Randomized Controlled Trial involved a control and an intervention group, with data collected at baseline, post-intervention, and a 6-month follow-up. The intervention group received an 8-week program via a mobile app that included motivational content (e.g., perceived threat) and volitional strategies (e.g., self-efficacy). Physical activity was measured using the IPAQ, and psychological constructs were assessed with a HAPA-based questionnaire.</p> Results <p>At baseline, there were no significant demographic differences between groups. Post-intervention, the intervention group showed significant increases in perceived threat (<i>P</i> = 0.000), outcome expectations (<i>P</i> = 0.04), and self-efficacy (<i>P</i> = 0.02) compared to the control group. The significant time x group interaction for perceived threat (<i>P</i> = 0.000) indicated a greater rate of change in the intervention group. While there were no significant group differences for perceived barriers, both groups showed significant changes over time. At the 6-month follow-up, the intervention group had a significantly greater increase in physical activity (<i>P</i> = 0.02) than the control group.</p> Conclusions <p>The findings suggest that a home-based virtual exercise program based on the HAPA is an effective and sustainable approach to improving physical activity and key psychological factors in patients with myocardial infarction. These results support the use of targeted digital interventions to enhance patient outcomes in cardiac rehabilitation.</p> Trial registration <p>This study has been registered in the Iranian Registry of Clinical Trials. Registration number: IRCT20210509051235N1. Date of registration: 2021-11-06. (<a href="https://irct.behdasht.gov.ir/trial/56204">https://irct.behdasht.gov.ir/trial/56204</a>)</p>