REN and hydrops fetalis: Various HF treatments exist and have shown success in reducing HF-associated mortality, such as implantable cardioverter defibrillators, heart transplant surgery, and numerous medications including ones that target the sympathetic nervous system (β-adrenergic receptor blockers), the renin-angiotensin aldosterone system (angiotensin converting enzyme inhibitors and angiotensin II receptor blockers) [14], and the pacemaker current of the sinoatrial cells (ivabradine) [15].