Physical activity is a key element in cardiac rehabilitation and prevention of cardiovascular mortality and hospitalizations. After cardiac rehabilitation programs end, physical activity levels and participation in continued cardiac rehabilitation declines.~The primary aim of this study is to evaluate the feasibility in terms of recruitment, retention, data completeness, intervention delivery and compliance, and acceptability of a mobile health intervention with text messages and behavior change theory in patients with cardiovascular disease for a duration of 3 months after completion of a cardiac rehabilitation program.~The study is a single-group multi-site feasibility trial. Participants will be recruited from phase II cardiac rehabilitation programs at Slagelse Hospital, the city of Slagelse (municipality), and Holbæk Hospital. Starting immediately after completion of cardiac rehabilitation, study participants will receive an intervention that consists of action planning, text messages, and coordinator support for a period of 12 weeks (see more details under 'Arms and Interventions'). The investigators base the intervention on a theoretical model of behavior change in the form of the Health Action Process Approach (HAPA). Behavior change techniques (BCTs) are used as part of the intervention. The intervention is an addition to standard practice and does not replace any existing treatment offers.~To evaluate the feasibility of the intervention and its readiness to be tested in a subsequent RCT design, the investigators have set progression criteria using a system of green (proceed to RCT), amber (amend when proceeding to RCT), or red (issue must be solved before proceeding to RCT). The progression criteria are listed under 'Primary Outcome Measures'.~Participants will wear accelerometers on thigh and wrist for 1 and 3 weeks, respectively, starting 1 week before end of cardiac rehabilitation. Baseline measurements and start of intervention is planned to be at the same time as cardiac rehabilitation ends. After 11 weeks of intervention, participants will attend a follow-up assessment, where participants will wear accelerometers on thigh and wrist again.
Physical activity is a key element in cardiac rehabilitation and prevention of cardiovascular mortality and hospitalizations. After cardiac rehabilitation programs end, physical activity levels and participation in continued cardiac rehabilitation declines. The aim of this study is to evaluate the feasibility a mobile health intervention with text messages and behavior change theory in patients with cardiovascular disease for a duration of 3 months after completion of a cardiac rehabilitation program. An intervention consisting of action planning, text messages, and coordinator support is tested in a feasibility trial design with 40 expected participants.