Aims: We aim to assess the theoretical impact of the atrial flow regulator (AFR) on survival in heart failure. Methods and results: The prospective, multicentre, open-label, non-randomised PRELIEVE study (NCT 03030274) assessed the safety and efficacy of the Occlutech AFR device in patients with symptomatic heart failure with reduced ejection fraction (HFrEF) (left ventricular ejection fraction (LVEF) ≥ 15% and <40%) or heart failure with preserved ejection fraction (HFpEF) (LVEF ≥40% and <70%) and elevated PCWP (≥15 mmHg at rest or ≥25 mmHg during exercise). In this analysis, after the first 60 patients completed 12 months of follow-up, the theoretical impact of AFR implantation on survival was assessed by comparing the observed mortality rate with the median predicted probability for one-year mortality. Each subject's risk of mortality was predicted from individual baseline data using the Meta-Analysis Global Group in Chronic HF (MAGGIC) prognostic model. A total of 87 patients (46% female, median age 69 years [IQR 62–74]) had undergone successful device implantation for the treatment of HFrEF (53%) and HFpEF (47%). Sixty patients had a complete 12 month follow-up. The median follow-up was 351 days (interquartile range [IQR] 202–370). Six (7%) patients died during follow-up (8.6 deaths per 100 patient-years; 95% confidence interval [CI] 2.7 to 15.5), all of which had HFrEF. The median predicted mortality rate for the overall study population was 12.2 deaths per 100 patient-years (95% CI 10.2 to 14.7). While the observed mortality rate (0 deaths per 100 patient-years) was significantly lower than the median predicted mortality rate (9.3 deaths per 100 patient-years; 95% CI 8.4 to 11.1) in patients with HFpEF (−9.3 deaths per 100 patient-years; 95% CI −11.1 to −8.4), there was no difference in patients with HFrEF (−3.6 deaths per 100 patient-years; 95% CI −9.5 to 3.0). Four deaths were HF-related deaths (5.7 HF-related deaths per 100 patient-years; 95% CI 1.4 to 11.9; 10.8 HF-related deaths per 100 patient-years; 95% CI 2.5 to 23.1 in the HFrEF subgroup). Conclusions: In patients with HFpEF, the mortality rate following AFR implantation was lower than the predicted mortality rate. Dedicated randomised, controlled trials are needed – and currently ongoing – to investigate whether the AFR improves mortality.