Abstract Background Heart failure affects 26 million people globally, and the optimal management of medicines is crucial for patients, particularly when their care is transferred between hospital and the community. Optimising clinical outcomes requires well-calibrated cross-organisational processes with staff and patients responding and adapting to medicines changes. The aim of this study was to assess the feasibility of implementing a complex intervention (the Medicines at Transitions Intervention; MaTI) co-designed by patients and healthcare staff. The purpose of the intervention was to optimise medicines management across the gaps between secondary and primary care when hospitals handover care. The study objectives were to (1) assess feasibility through meeting specified progression criteria to proceed to the trial, (2) assess if the intervention was acceptable to staff and patients, and (3) determine whether amendment or refinement would be needed to enhance the MaTI. Methods The feasibility of the MaTI was tested in three healthcare areas in the North of England between July and October 2017. Feasibility was measured and assessed through four agreed progression to trial criteria: (1) patient recruitment, (2) patient receipt of a medicines toolkit, (3) transfer of discharge information to community pharmacy, and (4) offer of a community pharmacy medicines review/discussion or medicines reconciliation. From the cardiology wards at each of the three NHS Acute Trusts (sites), 10 patients (aged ≥ 18 years) were recruited and introduced to the ‘My Medicines Toolkit’ (MMT). Patients were asked to identify their usual community pharmacy or nominate a pharmacy. Discharge information was transferred to the community pharmacy; pharmacists were asked to reconcile medicines and invited patients for a medicines use review (MUR) or discussion. At 1 month following discharge, all patients were sent three questionnaire sets: quality-of-life, healthcare utilisation, and a patient experience survey. In a purposive sample, 20 patients were invited to participate in a semi-structured interview about their experiences of the MaTI. Staff from hospital and primary care settings involved in patients’ care were invited to participate in a semi-structured interview. Patient and staff interviews were analysed using Framework Analysis. Questionnaire completion rates were recorded and data were descriptively analysed. Results Thirty-one patients were recruited across three sites. Eighteen staff and 18 patients took part in interviews, and 19 patients returned questionnaire sets. All four progression to trial criteria were met. We identified barriers to patient engagement with the intervention in hospital, which were compounded by patients’ focus on returning home. Some patients described not engaging in discussions with staff about medicines and lacking motivation to do so because they were preoccupied with returning home. Some patients were unable or unwilling to attend a community pharmacy in person for a medicines review. Roles and responsibilities for delivering the MaTI were different in the three sites, and staff reported variations in time spent on MaTI activities. Staff reported some work pressures and staff absences that limited the time they could spend talking to patients about their medicines. Clinical teams reported that recording a target dose for heart failure medicines in patient-held documentation was difficult as they did not always know the ideal or tolerable dose. The majority of patients reported receiving the patient-held documentation. More than two-thirds reported being offered a MUR by their community pharmacists. Conclusions Delivery of the Medicines at Transitions Intervention (MaTI) was feasible at all three sites, and progression to trial criteria were met. Refinements were found to be necessary to overcome identified barriers and strengthen delivery of all steps of the intervention. Necessary changes to the MaTI were identified along with amendments to the implementation plan for the subsequent trial. Future implementation needs to take into account the complexity of medicines management and adaptation to local context.