Assess comparative effectiveness, safety, and ethical implications of high‑intensity interval training (HIIT) versus moderate continuous training (MCT) for cardiovascular rehabilitation in older adults; evaluate clinical outcomes (VO2peak, functional capacity, hospital readmission, mortality), adverse events and contraindications across frailty and common comorbidities, adherence and monitoring needs, study quality and risk stratification, resource/cost considerations, and ethical issues (informed consent, autonomy, beneficence/nonmaleficence, equity, and shared decision‑making) to create evidence‑based, individualized recommendations for clinical practice and policy.