‘Water, salt, and blood pressure’ describes how the balance of water in the body is controlled by several hormones, including vasopressin (arginine vasopressin (AVP)). AVP reduces urine production by the kidneys and also causes small blood vessels to contract, raising blood pressure. Blood volume and pressure are also adjusted by changing the amount of sodium ions reclaimed by kidney nephrons. The renin–Ang-II–aldosterone hormone system balances blood volume and circulatory space to keep pressure stable when the volume and dilution of the blood change. But what happens if the concentration of salt (sodium and other ions) in the blood starts to rise? Is there a direct way to get rid of excess salt? A hormone secreted by the heart, called ANP, does exactly this.