The renal arteries normally arise off the left interior side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle. The renal arteries carry a large portion of total blood flow to the kidneys. Up to a third of total cardiac output can pass through the renal arteries to be filtered by the kidneys. Renal artery stenosis, or narrowing of one or both renal arteries will lead to hypertension as the affected kidneys release renin to increase blood pressure to preserve perfusion to the kidneys. RAS is typically diagnosed with duplex ultrasonography of the renal arteries. It is treated with the use of balloon angioplasty and stents, if necessary. Atherosclerosis can also affect the renal arteries and can lead to poor perfusion of the kidneys leading to reduced kidney function and, possibly, renal failure.