Abstract Background We recently showed that a lower high-density lipoprotein cholesterol (HDL-C) concentration was one of the strongest predictors of death or heart failure (HF) hospitalisation in patients with HF. In a follow-up study, we suggested that this association could be partly explained by HDL proteome composition. However, whether the emerging concept of HDL function contributes to prognosis of HF patients has not been addressed. Methods We measured three key HDL function metrics, namely cholesterol efflux, antioxidative capacity, and anti-inflammatory capacity, at baseline and after 9 months in 446 randomly selected HF patients from BIOSTAT-CHF. Additionally, the relationship between HDL functionality and HDL proteome composition was determined in 86 patients. Results From baseline to 9 months, HDL-C concentrations did not substantially change, but HDL-mediated cholesterol efflux and anti-inflammatory capacity had decreased (both P<0.001). In contrast, antioxidative capacity improved during the 9 months follow-up (P<0.001). Higher HDL-mediated cholesterol efflux was independently associated with lower risk of mortality after adjustment for BIOSTAT risk models and log HDL-C (HR=0.81 [95% CI: 0.71–0.92], P=0.001). Other functionality parameters were not associated with outcome. Several HDL proteins correlated with HDL functionality, mainly with cholesterol efflux, and apolipoprotein A1 emerged as the main protein associated with all three functionality parameters. Conclusions HDL-mediated cholesterol efflux and anti-inflammatory capacity significantly decreased over time in patients with HF. Better baseline cholesterol efflux was prospectively associated with reduced mortality during follow-up independent of HDL-C. Combined these data indicate that HDL function measurements have the potential to provide clinical information beyond static HDL-C concentrations in HF patients. Changes in HDL functionality over time Funding Acknowledgement Type of funding source: Public grant(s) – EU funding. Main funding source(s): European Commission