REN and hydrops fetalis: It is well-established that in patients with HF with reduced ejection fraction (HFrEF), renin-angiotensin-aldosterone system inhibitors (RAASi), e.g. ACE inhibitors (ACEi) and angiotensin-receptor blockers (ARBs), beta-blockers, mineralocorticoid-receptor antagonists (MRAs), the more recent combination sacubitril/valsartan, and sodium-glucose transport protein 2 inhibitors (regardless of diabetes status) markedly improve survival and reduce HF hospitalizations against placebo [4, 5].