ImportanceDespite high disease morbidity and mortality and complex treatment decisions, little is known about the medical and end-of-life decision-making preferences of adolescents and young adults (AYA) with advanced heart disease. AYA decision-making involvement is associated with important outcomes in other chronic illness groups.ObjectiveTo characterize decision-making preferences of AYAs with advanced heart disease and their parents and determine factors associated with these preferences.Design, Setting, and ParticipantsCross-sectional survey between July 2018 and April 2021 at a single-center heart failure/transplant service at a Midwestern US children’s hospital. Participants were AYAs aged 12 to 24 years with heart failure, listed for heart transplantation, or posttransplant with life-limiting complications and a parent/caregiver. Data were analyzed from May 2021 to June 2022.Main Outcomes and MeasuresSingle-item measure of medical decision-making preferences, MyCHATT, and Lyon Family-Centered Advance Care Planning Survey.ResultsFifty-six of 63 eligible patients enrolled in the study (88.9%) with 53 AYA-parent dyads. Median (IQR) patient age was 17.8 (15.8-19.0) years; 34 (64.2%) patients were male, and 40 patients (75.5%) identified as White and 13 patients (24.5%) identified as members of a racial or ethnic minority group or multiracial. The greatest proportion of AYA participants (24 of 53 participants [45.3%]) indicated a preference for active, patient-led decision-making specific to heart disease management, while the greatest proportion of parents (18 of 51 participants [35.3%]) preferred they and physician(s) make shared medical decisions on behalf of their AYA, representing AYA-parent decision-making discordance (χ2 = 11.7; P = .01). Most AYA participants stated a preference to discuss adverse effects or risks of treatment (46 of 53 participants [86.8%]), procedural and/or surgical details (45 of 53 participants [84.9%]), impact of condition on daily activities (48 of 53 participants [90.6%]), and their prognosis (42 of 53 participants [79.2%]). More than half of AYAs preferred to be involved in end-of-life decisions if very ill (30 of 53 participants [56.6%]). Longer time since cardiac diagnosis (r = 0.32; P = .02) and worse functional status (mean [SD] 4.3 [1.4] in New York Heart Association class III or IV vs 2.8 [1.8] in New York Heart Association class I or II; t-value = 2.7; P = .01) were associated with a preference for more active, patient-led decision-making.Conclusions and RelevanceIn this survey study, most AYAs with advanced heart disease favored active roles in medical decision-making. Interventions and educational efforts targeting clinicians, AYAs with heart disease, and their caregivers are needed to ensure they are meeting the decision-making and communication preferences of this patient population with complex disease and treatment courses.