Background: Whilst heart failure (HF) with preserved ejection fraction (HFpEF) affects almost 50 percent of the HF population, evidence-based treatment options remain limited. However, there is emerging evidence of the potential value of exercise-based cardiac rehabilitation. This study reports the process evaluation conducted as part of the REACH-HFpEF trial. Methods: Mixed methods process evaluation parallel to a single centre (Tayside, Scotland) pilot randomised controlled trial with quantitative assessment of intervention fidelity and a qualitative exploration of HFpEF patients' and caregivers' experiences. The Rehabilitation EnAblement in Chronic Heart Failure (REACH-HF) intervention consisted of self-help manual for patients and caregivers, facilitated over 12 weeks by trained healthcare professionals. Data included audio-recorded intervention sessions; demographic information; intervention fidelity scores; and qualitative interviews conducted following completion of intervention in a purposeful sample of 15 HFpEF patients and 7 caregivers, Results: Intervention fidelity analysis was indicative of the adequate delivery of the majority of the REACH-HF components, with three items relating caregiver involvement (addressing emotional consequences of being a caregiver, caregiver health and well-being, and closure of the session) scoring poorly. Qualitative interviews identified three key themes for patients and caregivers: (1) understanding their condition, (2) emotional consequences of HF, and (3) patients' and caregivers' responses to the REACH-HF intervention were uncovered by qualitative interviews.Conclusions: The REACH-HF home-based facilitated intervention for HFpEF appears feasible and well accepted model for delivery of a CR intervention, with the potential to address key unmet needs of patients and their caregivers who are often excluded from service provision and current CR programmes. Results inform a future full multicentre randomised clinical trial.