The number of patients with heart failure is expected to rise sharply owing to ageing populations, poor dietary habits, unhealthy lifestyles and improved survival rates from conditions such as hypertension and myocardial infarction. Heart failure is classified into two main types: heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF). These forms fundamentally differ, especially in how metabolism is regulated, but they also have shared features such as mitochondrial dysfunction. HFrEF is typically driven by neuroendocrine activation and mechanical strain, which demands a higher ATP production to sustain cardiac contraction. However, the primary energy source in a healthy heart (fatty acid β-oxidation) is often suppressed in HFrEF. Although glucose uptake increases in HFrEF, mitochondrial dysfunction disrupts glucose oxidation, and glycolysis and ketone oxidation only partially compensate for this imbalance. Conversely, HFpEF, particularly in individuals with metabolic diseases, such as obesity or type 2 diabetes mellitus, results from both mechanical and metabolic overload. Elevated glucose and lipid levels overwhelm normal metabolic pathways, leading to an accumulation of harmful metabolic byproducts that impair mitochondrial and cellular function. In this Review, we explore how disruptions in cardiac metabolism are not only markers of heart failure but also key drivers of disease progression. We also examine how metabolic intermediates influence signalling pathways that modify proteins and regulate gene expression in the heart. The growing recognition of the role of metabolic alterations in heart failure has led to groundbreaking treatments that target these metabolic disruptions, offering new hope for these patients.
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