Although the activation of these neurohormonal systems (i.e., renin–angiotensin–aldosterone system, sympathetic nervous system, and natriuretic peptides) preserves cardiovascular homeostasis in the beginning of HF and in the short term, a plethora of pre-clinical and clinical studies have demonstrated that the bioactive molecules generated by the activation of these systems are becoming toxic to the heart at higher levels [26]. Here, REN is linked to hydrops fetalis.