Background <p>Adolescents with congenital heart disease (CHD) face substantial challenges during the transition from pediatric to adult care. The STEPSTONES transition program is a person-centered, evidence-based intervention designed to support this transition, and has shown efficacy in improving patient empowerment and disease-related knowledge. However, implementing complex health interventions like the STEPSTONES transition program in real-world settings remains difficult. This study aimed to explore the barriers and facilitators to implementing the STEPSTONES transition program in Swedish pediatric cardiology clinics, using the Consolidated Framework for Implementation Research (CFIR).</p> Methods <p>A qualitative study was conducted in six university hospitals in Sweden prior to implementing the STEPSTONES transition program. Semi-structured interviews were carried out with 20 stakeholders, including nurses, physicians, managers, and a patient organization representative. Data were analyzed using reflexive thematic analysis, guided by the CFIR framework, covering five domains: intervention characteristics, outer setting, inner setting, characteristics of individuals, and implementation process.</p> Results <p>Facilitators to implementation of the transition program included the program’s clear structure, alignment with existing person-centered care practices, motivated local champions, and external demand for structured transitional care. Organizational readiness varied widely; clinics with managerial support, clear responsibilities, and engaged teams demonstrated higher preparedness. Barriers included limited time and resources, unclear professional roles (particularly regarding nurses’ responsibilities in delivering psychosocial components) and fragmented collaboration with adult care. Implementation efforts were often dependent on individual initiative rather than embedded in institutional routines.</p> Conclusions <p>Successful implementation of the STEPSTONES transition program requires attention to multilevel contextual factors, including organizational culture, interprofessional collaboration, and leadership support. Facilitation could be a key implementation strategy to address identified barriers and enhance uptake and sustainability. These findings offer valuable insights for the broader implementation of transition programs for young people with various chronic conditions in different settings.</p>