Exercise Intensity and Delivery in Cardiac Rehabilitation for Heart Failure: From Comparative Efficacy to Achieved Dose and Patient-Centred Implementation

Exercise-based cardiac rehabilitation improves functional capacity and quality of life in clinically stable patients with heart failure, but the comparative value of high-intensity interval training (HIIT) and moderate-intensity continuous training (MCT) remains uncertain. This narrative review updates evidence through August 2026 from PubMed/MEDLINE, publisher records, and professional-society sources, prioritizing randomized trials, systematic reviews, meta-analyses, and guidance documents. Rehabilitation probably reduces all-cause hospital admission and improves quality of life, although a short-term mortality reduction has not been established. Meta-analyses report a modest average HIIT advantage in peak oxygen uptake, about 1.5–1.8 mL/kg/min, but heterogeneity is substantial. SMARTEX-HF did not show HIIT superiority in heart failure with reduced ejection fraction, and OptimEx-Clin did not show a clinically important advantage in heart failure with preserved ejection fraction. Outcomes are influenced by achieved intensity, weekly duration, total work, adherence, frailty, comorbidity, supervision, and access. MCT remains a broadly applicable foundation, whereas supervised HIIT is reasonable for selected patients who can reach and recover from the intended workload. Home-based and hybrid models may extend access when assessment, feedback, safety escalation, and programme fidelity are maintained. Exercise prescription should be individualized around the dose patients can safely receive. Methods: This narrative review was updated through August 2026 using PubMed/MEDLINE and targeted searches of publisher and professional-society websites. Randomized trials, systematic reviews, meta-analyses, major guidance documents, and selected human mechanistic studies were prioritized. Numerical estimates were included only when traceable to a primary report or authoritative evidence synthesis. Because the review was not designed as a systematic review, no exhaustive study count or PRISMA flow diagram is claimed. Conclusion: HIIT is a useful option, not a universal replacement for MCT. A defensible prescription begins with clinical stability and functional assessment, selects a feasible initial modality, measures the achieved dose, and adapts the programme according to symptoms, response, preference, and access. The central clinical question is not which intensity is inherently best, but which programme can be delivered safely, accurately, and consistently to a particular patient.