REN and hydrops fetalis: The studies on patients with low- and high-output HF, support the idea that preservation or maintenance of the arterial blood pressure is the main trigger for the development of neurohormonal overactivity (activation of the sympathetic nervous system (SNS) and the renin-angiotensin aldosterone system (RAAS)) [13,14]) signaling to the kidney to retain sodium and water which seen in all forms of HF [15].