ACE inhibitor (āˌsēˌēˈ, ās) [key] or angiotensin-converting enzyme inhibitor ănˌjēōtĕnˈsĭn, drug used to reduce elevated blood pressure (see hypertension), to treat congestive heart failure, and to alleviate strain on hearts damaged as a result of a heart attack (see infarction). ACE inhibitors block production of an enzyme that helps convert the protein angiotensin 1 into angiotensin 2, a protein that makes blood vessels constrict and promotes retention of fluid, raising blood pressure. Thus ACE inhibitors act to widen the blood vessels and make it easier for the heart to pump blood through the body. captopril (Capoten), ramipril (Altace), and enalapril (Vasotec) are commonly used ACE inhibitors. Angiotensin-receptor blockers (ARBs), such as losartan (Cozaar) and valsartan (Diovan), reduce hypertension by displacing angiotensin 2 from receptors on the surface of cells. ARBs are used as alternatives to the less expensive ACE inhibitors because they have fewer side effects.