Background: Cardiac rehabilitation (CR) is a comprehensive secondary prevention program involving exercise training, behavioral activation, and psychosocial support following cardiac events such as myocardial infarction, coronary revascularization, valve replacement. Randomized clinical trials (RCT) have demonstrated lower mortality and greater physical, mental, and social functioning in patients who participate in CR vs. usual care. However, the long-term mortality benefit of CR is directly proportional to the number of sessions completed, and less than half of Veterans who enroll in CR complete the recommended number of sessions. Significance: Home-based CR (HBCR) is an alternative to traditional CR programs that has comparable efficacy in improving morbidity/mortality and increases access to critical services. Improving participation in home-based CR has been identified as a major priority by the National Director of Cardiology. We propose to test a novel and easily scalable intervention to increase HBCR adherence and improve functional capacity/ physical activity in Veterans at risk for secondary cardiac events. This project addresses a major quality gap and aligns closely with VHA Modernization priorities of: a) virtual care/telehealth utilization; b) digital transformation; and c) MISSION Act implementation by offering high quality, easy to access care. Innovation and Impact: There is major potential to improve Veteran engagement in CR by combining digital coaching (d-Coaching) with existing VA-supported technologies. Our theory-based intervention targets a critical component of successful CR engagement that is not available through traditional programs: virtual social support through a social network. In addition, we propose to improve self-efficacy and self-regulation through interactive digital multi-media education, personalized feedback, and motivation so that Veterans can complete the prescribed HBCR program and maintain physical activity long-term. The innovative features include: 1) the use of the VA-approved MOVN mobile app to deliver the d-Coaching intervention and provide peer social networks; 2) interactive tailored messages via Annie text messaging to reinforce Veteran-centered goals, learning, and support; and 3) optional participation in a Fitbit private group leaderboard. Specific Aims: Aim 1: Determine the effect of the d-Coaching intervention on the number of completed HBCR sessions over 3 months. Aim 2: Determine the effect of the d-Coaching intervention on: a) functional capacity (6-minute walk test), b) physical activity (daily step counts, sedentary time), c) psychosocial outcomes (depressive symptoms, quality of life), and d) clinical outcomes (HbA1C, lipids) and rehospitalization/ mortality. Aim 3: Determine the effect of the d-Coaching intervention on social cognitive factors of self-efficacy, self-regulation, and perceived social support. Aim 3a: Evaluate the extent to which self-efficacy, self-regulation, and perc...