The goal of this clinical trial is to learn whether a Nintendo Switch-based exergame physical activity program can help children and adolescents with congenital heart disease increase their physical activity. It will also learn about the safety, acceptability, and feasibility of this program. The study will include children and adolescents aged 8 to 18 years who have congenital heart disease, have received surgical or interventional treatment, and are clinically stable.

The main questions it aims to answer are:

Does the exergame-based program increase the amount of time participants spend in moderate-to-vigorous physical activity each day? Is the exergame-based program safe, acceptable, and feasible for children and adolescents with congenital heart disease?

All participants will receive the same exergame-based physical activity program. Researchers will use different baseline observation periods to help understand whether changes in physical activity happen after the program starts.

Participants will:

Wear an activity monitor to measure daily physical activity. Complete a baseline observation period lasting 7, 14, or 21 days. Take part in a 12-week Nintendo Switch-based exergame physical activity program with guidance, goal setting, self-monitoring, feedback, and caregiver support.

Complete a 2-week observation period after the program to see whether physical activity changes are maintained.

Complete study assessments at screening, the end of baseline, week 4, week 8, week 12, and the end of the observation period.

Researchers will also collect information on step counts, energy expenditure, self-reported physical activity, exercise capacity, quality of life, adherence, acceptability, and adverse events.

Regular physical activity is important for physical function, exercise capacity, psychosocial development, quality of life, and long-term cardiovascular health in children and adolescents with congenital heart disease. However, this population may experience insufficient physical activity and increased sedentary behavior because of disease-related factors, parental concerns about exercise risk, long-term perceptions of exercise restriction, reduced physical fitness, and psychosocial barriers.

Exergames combine physical movement with interactive game-based tasks and may be suitable for children and adolescents because they are engaging, easy to access, and provide immediate feedback. Nintendo Switch motion-sensing games can incorporate activities such as jumping, striking, balance, coordination, and whole-body movement into game tasks. For clinically stable children and adolescents with congenital heart disease, exergames may offer a feasible approach to promoting moderate-intensity physical activity in home settings when appropriate safety screening and guidance are provided.

This study will evaluate an exergame-based physical activity promotion intervention combined with behavioral support strategies. The intervention is designed to promote physical activity through individualized exercise guidance, goal setting, self-monitoring, feedback reinforcement, caregiver support, and safety monitoring. The intervention will be delivered over 12 weeks and will be adjusted according to each participant's clinical condition, exercise tolerance, participation experience, and adherence.

A multiple-baseline single-case experimental design will be used because children and adolescents with congenital heart disease may differ substantially in diagnosis, post-treatment status, exercise capacity, family support, and behavioral response. Each participant will serve as his or her own control. Participants will be randomly assigned to one of three baseline lengths: 7 days, 14 days, or 21 days. This staggered introduction of the intervention is intended to help distinguish intervention-related changes from natural changes over time.

The study will follow an A-B-A' structure. Phase A is the baseline phase, during which no formal exergame intervention will be provided and physical activity will be monitored continuously. Phase B is the 12-week intervention phase, during which participants will receive the Nintendo Switch-based exergame physical activity promotion intervention with behavioral support. Phase A' is a 2-week observation phase, during which intensive intervention support will stop and physical activity monitoring will continue to assess maintenance of intervention effects.

Participants will complete six assessment visits or time points: screening and baseline assessment, end of baseline, week 4 of intervention, week 8 of intervention, week 12 of intervention, and the end of the 2-week observation phase. Physical activity will be monitored repeatedly from baseline through the observation phase. The primary outcome is daily moderate-to-vigorous physical activity in minutes per day, measured using an ActiGraph wGT3X-BT triaxial accelerometer. Secondary outcomes include daily step counts, energy expenditure, self-reported physical activity, behavioral change-related psychological factors, cardiopulmonary fitness, 6-minute walk distance, heart rate-related indicators, body composition, and health-related quality of life. Feasibility, acceptability, adherence, and adverse events will also be recorded.

Data will be analyzed at both the individual and aggregated levels. Individual-level analyses will include visual analysis of level, trend, variability or stability, immediacy of effect, overlap, and consistency of patterns across participants. Time-series or segmented regression methods may be used to estimate level and trend changes across phases. Aggregated analyses will use linear mixed-effects models, with hierarchical Bayesian models considered as supplementary analyses, to estimate overall intervention effects and individual differences.

This study will provide preliminary evidence on the feasibility, acceptability, safety, and potential effectiveness of an exergame-based physical activity promotion intervention for children and adolescents with congenital heart disease. The findings may inform the development and optimization of digital physical activity promotion and rehabilitation strategies for this population.

Inclusion Criteria:

1. aged 8-18 years, with a confirmed diagnosis of congenital heart disease and a history of cardiac surgery or catheter-based intervention;
2. at least 3 months since the most recent surgery or intervention, with a clinically stable condition and no planned reintervention in the near future;
3. deemed by a pediatric cardiologist to be suitable for regular physical activity or low-to-moderate to moderate-to-vigorous physical activity;
4. presenting with insufficient physical activity and/or impaired exercise capacity, defined by at least one of the following: failure to meet the recommended physical activity level for children and adolescents (ie, an average of 60 minutes of moderate-to-vigorous physical activity per day), objectively impaired exercise capacity (eg, peak oxygen uptake <80% of predicted and/or anaerobic threshold <55% of predicted), or reduced exercise tolerance indicated by the 6-minute walk test, physical fitness assessment, or clinical exercise evaluation;
5. having basic cognitive and communication abilities sufficient to understand instructions and complete questionnaires, trial sessions, and training tasks;
6. willingness of both the child and the guardian to participate, with written informed consent obtained;
7. availability of basic family conditions to support intervention delivery, including access to smart devices and/or game equipment, internet access, and at least one caregiver able to provide support.

Exclusion Criteria:

1. clear contraindications to exercise, such as uncontrolled arrhythmia, overt heart failure, severe pulmonary hypertension, or recent hemodynamic instability;
2. severe comorbidities that substantially interfere with exercise performance, such as serious neurological disorders, severe musculoskeletal disorders, or other conditions markedly limiting physical activity;
3. participation within the previous 3 months in another systematic intervention likely to substantially influence physical activity or exercise capacity;
4. any condition, as comprehensively judged by the research team, that may affect participant safety, intervention implementation, the quality of physical activity monitoring data, or completion of questionnaires or follow-up, including refusal to wear the monitoring device, refusal to complete follow-up, or evident risk of poor adherence.

Individual participant data will not be publicly shared because the study involves minors with congenital heart disease, a small sample size, and intensive longitudinal physical activity data, which may increase the risk of participant re-identification even after de-identification. Aggregate results will be reported in publications. Reasonable requests for additional information may be considered by the principal investigator and the ethics committee in accordance with institutional policies and participant privacy protections.