Biomarkers of Cardiac Metabolic Flexibility in Health, HFrEF and HFpEF.

Cardiac metabolic flexibility is a key determinant of myocardial energetic resilience. In heart failure with reduced ejection fraction (HFrEF), intrinsic mitochondrial dysfunction and lipotoxicity compromise oxidative capacity. In contrast, heart failure with preserved ejection fraction (HFpEF) is orchestrated primarily by systemic comorbidities and coronary microvascular dysfunction, which decouple glycolysis from glucose oxidation. This review integrates these distinct pathophysiologies into a comprehensive biomarker framework. Beyond core hemodynamic markers, we detail indices of metabolic flux (ketones, acylcarnitines, branched-chain amino acids), endothelial injury, and fibrosis. We further prose a shift from static, isolated measurements to dynamic functional profiling using standardized challenges (e.g., mixed-meal or exercise tests) to quantify metabolic suppression and recovery kinetics. This structured hierarchy enables phenotype-tailored risk stratification and guides mechanism-based precision therapies in the era of personalized medicine.