Current estimates indicate more than 2 million individuals in the United States have CHD. CHD survivors are now living well into adulthood, including those with moderate and complex forms of CHD, who previously did not survive childhood. However, adult CHD survivors are now encountering cardiovascular comorbidities, such as coronary disease and hypertension, costing more than $3.16 billion annually in hospitalizations and resulting in premature death. The benefits of physical activity for preventing coronary artery disease and other cardiac comorbidities are well-known. For CHD survivors, the benefits of physical activity for preventing morbidity and premature mortality have also been emphasized. Despite strong evidence for physical activity preventing and treating acquired cardiovascular comorbidities among CHD survivors, adolescents and young adults (AYAs) with CHD do not meet recommended activity levels. The CHD-PAL intervention aims to provide individualized guidance on safe forms of physical activity that is delivered by trained allied health interventionists.

The CHD-PAL intervention is informed by the Theory of Planned Behavior (TPB) which has been used as a framework for lifestyle interventions, including among adults with heart failure and adolescents. Additionally, the CHD-PAL intervention implements goal-setting (or developing action plans) and self-monitoring, both of which are key for enacting the behavior within the TPB.

Investigators will randomize (1:1) 144 AYAs (ages 15-25) with moderate and complex CHD who spend \<=30 minutes/day in moderate to vigorous physical activity (MVPA) to 1 of 2 arms: CHD-PAL or attention control (Control). Both arms will receive a Fitbit® and a tailored exercise prescription. Those in CHD-PAL will also receive a 20-week videoconferencing-administered intervention that includes 9, 20 to 30-minute sessions designed to increase positive attitudes towards, subjective norms for, and perceived control for engaging in physical activity. Self-monitoring and goal-setting will also be encouraged to help enact behavior change. Controls will receive the same number/frequency of videoconferencing contacts to discuss the Fitbit and exercise prescription, as well as general healthy living, without addressing the TPB hypothesized mechanisms. Controls will also not be directed to self-monitor or engage in goal-setting. All participants will receive text messages from interventionists to either reinforce session content and inquire about progress towards goals (CHD-PAL) or to remind participants to wear the Fitbit (Control). Randomization will be stratified by gender and age using randomly varying block sizes of 4 to 6. MVPA, as measured with a research-grade accelerometer, will be assessed at baseline (T1), post-intervention (T3; 20 weeks after baseline), interim follow-up (T4; 20 weeks post-intervention), and follow-up (T5; 40 weeks post-intervention). TPB mechanisms will be similarly assessed, with the addition of an interim assessment during the intervention (T2; 10 weeks after baseline). Cardiorespiratory fitness (peak volume of oxygen consumption (VO2) and metabolic equivalent (METs)), as assessed via stress testing, will be measured at T1 and T3 as exploratory secondary outcomes.

The primary aim is to determine the efficacy of the CHD-PAL intervention on change in time spent in moderate to vigorous physical activity (MVPA) for AYAs with moderate and complex CHD. The secondary aim is to explore change in the TPB mechanisms and their relevance to change in MVPA. The tertiary aim is exploring the impact of CHD-PAL on cardiorespiratory fitness.