Carnitine is a friend in HFpEF and foe in HFrEF.

Heart failure (HF) is a global concern, particularly HF with preserved ejection fraction (HFpEF), lacking effective treatments. Understanding the differences of metabolic profiles between HFpEF and HFrEF (heart failure with reduced ejection fraction) patients is crucial for therapeutic advancements. In this study, pseudotargeted metabolomics was employed to analyze for disparities of plasma metabolic profiles between HFpEF and HFrEF in two cohorts: discovery (n = 514) and validation (n = 3368). Plasma-free carnitine levels were significant changed in HF patients. A non-linear and U-shaped (for HFpEF) or J-shaped (for HFrEF) association between circulating free carnitine levels and the composite risk of cardiac events were observed. Interestingly, HFpEF patients with low free carnitine (≤40.18 μmol/L) displayed a poorer survival, contrasting with HFrEF where higher levels (≥35.67 μmol/L) were linked to poorer outcomes, indicating distinct metabolism pathways. In conclusion, these findings offer insights into HFpEF metabolic profiles, suggesting potential therapeutic targets.