REN and hydrops fetalis: sHFrEF is characterized by the chronic pathological activation of the classical renin–angiotensin–aldosterone system (RAAS), dysregulation of the protective RAAS arm (Ang 1–7/MAS), and impairment of the natriuretic peptide (NP) system, which promotes salt and water retention leading to clinical HF signs and symptoms from edema, a decline in the quality of life, and premature death [9,11,12,13,14,15,16,17,18,19].