Background: Cardiovascular disease (CVD) is the leading cause of premature death and disability in Europe. Cardiac Rehabilitation (CR) can reduce the impact of CVD by lowering mortality and morbidity rates and promoting healthy active lifestyles. Yet adherence within CR is low. Research suggests that mHealth interventions are useful in supporting the self-management of chronic disease. The purpose of this research is to report on the development of an mHealth intervention. Methods: For the intervention development the Medical Research Council’s formative process consisting of 4 stages; i) development, ii) feasibility/piloting, iii) evaluation and iv) implementation will be used to develop a theoretically informed Android App to enhance disease self-management and quality of life in CVD. Like CR it will use exercise as its main modality, and provide advice on other health behaviours. Results: A systematic review of the use of behaviour change techniques (BCTs) in physical activity eHealth interventions for CVD patients has been conducted. Seven electronic databases yielded 987 articles, 97 of which met the inclusion criteria for full text review. A multidisciplinary team comprised of exercise scientists, health behaviour change and technology specialists are using this information to develop the intervention prototype. Stage one will be followed by qualitative research, where end-users will be asked to examine the intervention in order to determine its feasibility and acceptability, to ultimately improve its efficacy through a co-design process. Conclusion: Preliminary findings and systematic review protocol will be reported as per the PRISMA guidelines, ultimately aiding the development of the MedFit app.