Complex eHealth interventions--featuring multiple components within dynamic systems--are used for healthcare improvement. Public-private partnerships (PPPs), combining resources, expertise, and technology, are crucial in this context. Yet, integrating these interventions into practice remains challenging. This study identifies barriers and facilitators affecting implementation of the BENEFIT programme, a complex eHealth intervention targeting cardiovascular disease patients, by PPP within practice. A qualitative study design was employed. Ten key stakeholders from four cardiac rehabilitation (CR) sites, who were all PPP partners involved in developing and implementing the BENEFIT programme, were interviewed semistructured. Transcripts were analysed using Consolidated Framework for Implementation Research. Facilitators included programme adaptability, communication and planning within teams, digital healthcare needs, dedicated PPP leadership, PPP meeting structure and PPP's ability to quickly modify the implementation strategy. Barriers involved specific PPP challenges (frequently changing roles, unclear roles and responsibilities and limited staffing), workplace disruptions, poor information technology (IT) integration, and ambiguous implementation goals amongst CR sites. This case study highlights challenges in implementing complex eHealth interventions by PPPs within practice. The findings underscore the need for a comprehensive implementation approach considering specific PPP dynamics, including combined expertise and resources, transparent role definition, sufficient staffing, clear goal communication and adaptable strategies for sustainable implementation.