The renin–angiotensin system is a master regulator of human physiology. It controls blood pressure and fluid and electrolyte balance through coordinated effects on the heart, blood vessels, and kidneys. In the classic pathway of the renin–angiotensin system, renin is secreted from the juxtaglomerular apparatus of the kidney and acts on the circulating precursor angiotensinogen to generate angiotensin I (Figure 1). Angiotensin I has little effect on blood pressure and is converted in the lungs by angiotensin-converting enzyme (ACE) to angiotensin II. A potent vasopressor, angiotensin II acts on the heart and the kidneys by binding to the G protein–coupled receptors . . .