Background Patients with myocardial infarction (MI) seldom reach recommended targets for secondary prevention. This study evaluated a smartphone application (“app”) aimed at improving treatment adherence and cardiovascular lifestyle in MI patients. Design Multicenter, randomized trial. Methods A total of 174 ticagrelor-treated MI patients were randomized to either an interactive patient support tool (active group) or a simplified tool (control group) in addition to usual post-MI care. Primary end point was a composite nonadherence score measuring patient-registered ticagrelor adherence, defined as a combination of adherence failure events (2 missed doses registered in 7-day cycles) and treatment gaps (4 consecutive missed doses). Secondary end points included change in cardiovascular risk factors, quality of life (European Quality of Life–5 Dimensions), and patient device satisfaction (System Usability Scale). Results Patient mean age was 58 years, 81% were men, and 21% were current smokers. At 6 months, greater patient-registered drug adherence was achieved in the active vs the control group (nonadherence score: 16.6 vs 22.8 P = .025). Numerically, the active group was associated with higher degree of smoking cessation, increased physical activity, and change in quality of life; however, this did not reach statistical significance. Patient satisfaction was significantly higher in the active vs the control group (system usability score: 87.3 vs 78.1 P = .001). Conclusions In MI patients, use of an interactive patient support tool improved patient self-reported drug adherence and may be associated with a trend toward improved cardiovascular lifestyle changes and quality of life. Use of a disease-specific interactive patient support tool may be an appreciated, simple, and promising complement to standard secondary prevention.