REN and heart failure: According to the American Heart Association/American College of Cardiology/Heart Failure Society of America (AHA/ACC/HFSA) and the European Society of Cardiology (ESC) guidelines, implementation of quadruple therapy with renin–angiotensin–aldosterone system (RAAS) inhibitors (including ARNIs or ACEIs or ARBs), β-blockers, MRAs and SGLT2 inhibitors is recommended as the first step in patients with HFrEF to ameliorate clinical progression, reduce HF hospitalisation, and improve survival as early as within 30 days of drug initiation [10, 12, 57].