Aldosterone (ALD) is produced by the adrenal glands and it is a hormone that plays an important role in maintaining normal sodium and potassium concentrations in blood. Aldosterone stimulates the retention of sodium (salt) and the excretion of potassium by the kidneys. Aldosterone is controlled by the Renin-Angiotensin-Aldosterone system (RAAS). The kidneys release renin when there is a drop in blood pressure or a decrease in sodium chloride concentration in the tubules in the kidney. Renin cleaves the blood protein angiotensinogen to form angiotensin I(Al), which is then converted by a second enzyme to angiotensin II (A II}. Angiotensin II causes blood vessels to constrict, and it stimulates aldosterone production. Overall, this raises blood pressure and keeps sodium and potassium at normal levels. A variety of conditions can lead to aldosterone overproduction or underproduction. Since Angiotensin and aldosterone are so closely related, both substances are often tested together to identify the cause of heart diseases.