Purpose: Cardiovascular disease (CVD) is the leading cause of premature death and disability in Europe. Effective exercise-based cardiac rehabilitation (CR) can improve mortality and morbidity rates, yet uptake of community-based CR is low (1). PATHway (Physical Activity Towards Health) is a technology-enabled lifestyle behaviour change intervention designed to enhance patient self-management of CVD through adherence to physical activity and other health behaviours. This paper explains the co-design and user validation process that is being employed for the development of the PATHway platform. Methods: CVD patients from a) hospital-based CR and b) community-based CR across two sites (Dublin, Ireland; Leuven, Belgium) are invited to participate in the study. To facilitate an iterative process, three separate rounds of semi-structured interviews, a total of twelve focus groups (4 groups x 3 rounds) are planned between February and April 2016. In round one interviews, participants were exposed to the PATHway intervention and system designed by the research team, and feedback was elicited. Interviews were audio-recorded, transcribedand content analysed. Key recommendations regarding technical and intervention content were identified and are currently being used by the research team to improve the PATHway system. Completion of the interviews is due for April 2016 Results: Round one data indicated that i) tailoring intervention content for exercise prescription and health behaviour change was important; ii) further health information and monitoring through the system was valuable, and iii) the potential for patients to be connected with their healthcare professionals was appealing. Technical recommendations included amending the avatar display to reflect an average BMI and be ‘more human-like’. Additional behaviour change recommendations included stressing the importance of positive reinforcement even when a participant is not meeting set goals. Conclusions: An iterative co-design and user validation process can be a vital component of the development of complex behavioural interventions for CVD patients. This project has received funding from the European Union’s Horizon 2020 Framework Programme for Research and Innovation Action under Grant Agreement no. 643491. PATHway: Technology enabled behavioural change as a pathway towards better self-management of CVD (www.pathway2health.eu)