The Second Universal Definition of Heart Failure (HF) published in 2026 updates the 2021 consensus framework, which redefines diagnostic criteria, disease trajectories, and phenotypic classifications.^1,2 It replaces rigid ejection fraction cutoffs with three simplified, clinically actionable categories: reduced, preserved, and improved ejection fraction.¹ Additionally, it introduces a universal classification of pathogenic causes beyond basic ischemic categories, and formalizes disease trajectories including remission and recovery.¹ Finally, the consensus emphasizes the importance of recognizing diagnostic mimics and addressing social determinants to establish a standardized, global approach to management.¹

HF is a rapidly growing global pandemic affecting an estimated 64 million people worldwide.³ Overall prevalence is expected to rise, largely driven by an aging population.³ In Hong Kong, local prevalence is reported at 2%-3%, though global data suggest that half of all HF cases remain undetected.³ Notably, phenotypic distribution is shifting; while the prevalence of HF with reduced ejection fraction (HFrEF) is stabilizing or declining, the prevalence of HF with preserved ejection fraction (HFpEF) is increasing.³ While these epidemiological trends were established under the 2021 framework, the release of the 2026 consensus statement introduces updated staging and classification parameters to better reflect modern practice.¹

The Second Universal Definition provides an updated, standardized paradigm for clinicians and researchers worldwide.¹ Building upon the 2021 framework, HF remains defined as a clinical syndrome caused by structural or functional cardiac abnormalities, corroborated by elevated natriuretic peptide levels or objective evidence of pulmonary or systemic congestion.¹ The four-tier staging system—stage A (at risk), stage B (pre-HF featuring subclinical structural or functional changes or elevated biomarkers), stage C (symptomatic HF), and stage D (advanced disease requiring specialized interventions)—remains fundamental.¹

A major shift in the updated consensus concerns the subclassification of HF phenotypes relative to left ventricular ejection fraction (LVEF).¹ While the 2021 definition relied on rigid numerical cutoffs, defining HFrEF as ≤40%, mildly reduced (HFmrEF) as 41% to 49%, and HFpEF as ≥50%, the 2026 framework moves away from strict numerical boundaries.^1,2 Recognizing measurement variability across modalities, sex-specific differences (lower normal limits of 53% in women and 52% in men), and higher normal thresholds in certain Asian populations, the updated scheme reclassifies phenotypes into three actionable categories: HFrEF, HFpEF, and HF with improved ejection fraction (HFimpEF), integrating intermediate EF ranges into a continuous, treatment-guided spectrum.¹ This shift facilitates appropriate therapy across broader EF ranges.¹

Beyond ejection fraction, the 2026 statement introduces a comprehensive universal classification of underlying causes, replacing the oversimplified dichotomy of ischemic versus non-ischemic cardiomyopathy.¹ This system categorizes etiologies into distinct pathogenic groups, such as hypertensive, infiltrative, toxic, heritable, metabolic, inflammatory, and arrhythmia-related cardiomyopathies, encouraging targeted disease-modifying therapies.¹ Furthermore, the consensus clarifies dynamic disease trajectories by formalizing the concepts of improvement, remission, and recovery.¹ Improvement describes a ≥10-point increase in LVEF to >40% despite persistent abnormalities, whereas remission denotes normalized EF and minimal symptoms while retaining vulnerability to relapse.¹ True recovery, sustained normalization of structure, function, biomarkers, and symptoms, occurs in only a minority.¹ The updated definition also distinguishes worsening HF, defined as progressive symptom deterioration in a patient with a prior diagnosis, from decompensated HF, which specifically requires therapeutic escalation or rescue care, such as intravenous diuretics or hospitalization.¹

Additionally, the consensus cautions clinicians regarding diagnostic mimics, such as exertional myocardial ischemia, chronic kidney disease, severe obesity, deconditioning, and pregnancy-related physiological changes, which require careful differentiation from primary HF.¹ By incorporating the impact of social determinants of health and global geographic variations in cardiovascular disease patterns, the Second Universal Definition provides an adaptable, standardized approach aimed at optimizing global prevention, early detection, and individualized management.¹

By replacing rigid ejection fraction cutoffs with a flexible, treatment-guided spectrum while formalizing dynamic trajectories like remission and recovery, the Second Universal Definition updates HF management.¹ Ultimately, this comprehensive framework establishes a standardized global approach to refine early detection, address diagnostic mimics, and deliver individualized care.¹