In cardiac rehabilitation programs, patients learn how to adopt a healthier lifestyle, including regular, strenuous physical activity. Long-term success is only modest despite good intentions. To improve exercise adherence, a 3-group experiment was designed that included innovative psychological interventions. All 3 groups underwent a standard care rehabilitation program. Patients in the 2 treatment groups were instructed not only to produce detailed action plans but also to develop barrier-focused mental strategies. On top of this, in 1 of these groups a weekly diary was kept for 6 weeks to increase a sense of action control. At the end of a standard cardiac rehabilitation program, 240 patients were randomly assigned to these treatment groups plus a standard care control group. Treatments resulted in more physical activity at follow-up and better adherence to recommended levels of exercise intensity. Moreover, self-regulatory skills such as planning and action control were improved by the treatments. Follow-up analyses demonstrated the mediating mechanisms of self-regulatory skills in the process of physical exercise maintenance. Findings imply that interventions targeting self-regulatory skills can enable post-rehabilitation patients to reduce behavioral risk factors and facilitate intended lifestyle changes.