BACKGROUND: We report findings of a qualitative evaluation of fixed-dose combination therapy for patients with established atherosclerotic cardiovascular disease (ASCVD) attending Médecins Sans Frontières (MSF) clinics in Lebanon. Cardiovascular disease is a leading cause of death and disability worldwide, and humanitarian actors are increasingly faced with the challenge of providing care for chronic diseases such as ASCVD in settings where health systems are disrupted. Secondary prevention strategies, involving 3-5 medications, are known to be effective for patients at risk of heart attack or stroke, but supply and adherence are challenging in humanitarian settings. Fixed dose combination therapy, combining two or more medications in one tablet, may be a strategy to address this. METHODS: The evaluation was nested within a prospective mixed-methods study in which eligible ASCVD patients were followed for 1 year during (i) 6 months of usual care then (ii) 6 months of fixed dose combination (FDC) therapy. After 1 year, we conducted in-depth interviews with a purposive sample of patients, MSF staff and external stakeholders. Interviews focused on acceptability and sustainability of the fixed dose therapy intervention. Interview data were analysed thematically, informed by thea Theoretical Framework of Acceptability. Additional attention was paid to non-typical cases in order to test and strengthen analysis. RESULTS: Patients and health care providers were positive about the FDC intervention. For patients, acceptability was related to ease of treatment and trust in MSF staff, while, for staff, it was related to perceived improvements in adherence, having a good understanding of the medication and its use, and fitting well with their priorities for patient's wellbeing. External stakeholders were less familiar with FDC therapy. While external clinicals expressed concerns about treatment inflexibility, non-clinician stakeholder interviews suggested that cost-effectiveness would have a major influence on FDC therapy acceptability. Sustainability was tied to the future role of MSF care provision and coherence with the local health system. CONCLUSIONS: For patients and clinic staff, FDC was an acceptable treatment approach for secondary prevention of ASCVD disease in two MSF clinics in Lebanon. Sustainability is more complex and calls for better alignment of care with public systems.