REN and hydrops fetalis: Early HF trials defined HF using a reduced left ventricular ejection fraction (LVEF) as an entry criterion, leading to the distinction of HFrEF from HFpEF since large trials of medications (e.g., renin-angiotensin-aldosterone system blockers) that showed improved survival in HFrEF later failed to improve outcomes in similar trials for HFpEF [5].