Establishing Efficacy for the Congenital Heart Disease Physical Activity Lifestyle Intervention - PROJECT SUMMARY/ABSTRACT As congenital heart disease (CHD) survivors enter adulthood, they have a greater risk for developing acquired cardiovascular complications (e.g., hypertension and coronary artery disease). These comorbidities are amenable to lifestyle changes, such as increasing physical activity, yet adolescence and young adulthood are when physical activity rates begin declining. The CHD Physical Activity Lifestyle intervention (CHD-PAL) targets transition-age CHD survivors, using an engaging face-to-face videoconferencing format that this theory- informed and tailored to the unique physiology and activity needs of each participant. The CHD-PAL videoconferencing sessions address elements of the Theory of Planned Behavior (TPB; i.e., attitudes, subjective norms, and perceived control for engaging in a behavior) and implements self-monitoring and goal- setting techniques. The CHD-PAL feasibility/preliminary efficacy trials indicated that CHD-PAL is feasible for AYAs and that CHD-PAL increases time spent in moderate-to-vigorous physical activity (MVPA) as compared to the control group for AYAs who engage in lower levels of physical activity. However, a larger trial is needed to determine the impact of CHD-PAL on MVPA, purported mechanisms (i.e., elements of TPB), and health outcomes among AYAs with CHD. The primary objective of the current study is to determine the impact of CHD-PAL on change in MVPA among 144 AYAs (ages 15-25) with moderate and complex forms of CHD who will be randomized to 1 of 2 arms: CHD-PAL or attention control (Control). CHD-PAL consists of a 20-week videoconferencing-administered physical activity intervention (9, 20- to 30-minute sessions; Fitbit® to self- monitor and set goals) with an interventionist (“coach”). Control participants will receive the same number and frequency of contacts with a coach using the same modality to discuss using the Fitbit without addressing the TPB hypothesized mechanisms or being directed to self-monitor or set goals. The primary study outcome is change in MVPA as measured by an accelerometer. Change in the TPB hypothesized mechanisms will be assessed as secondary outcomes and change in cardiorespiratory fitness (i.e., peak VO2 and METs) will be explored. Our specific aims are to (1) determine the impact of CHD-PAL on change in MVPA and examine effect durability, (2) explore change in the TPB mechanisms and their relevance to change MVPA, and (3) explore the impact of CHD-PAL on change in cardiorespiratory fitness. The current study is the next step in an iterative process to refine CHD-PAL before multisite assessment of longer-term health implications and cost effectiveness of the intervention for AYAs with CHD in a clinical setting. Ultimately, this research has the potential to improve cardiovascular outcomes for transition-aged CHD survivors, an understudied growing population in need, as well as other pediatric chronic conditions with cardiopulmonary risk.