Enalapril is an angiotensin converting enzyme (ACE) inhibitor used in the treatment of hypertension, diabetic nephropathy, and some types of chronic heart failure. ACE converts the peptide hormone angiotensin I to angiotensin II. One of the actions of angiotensin II is the vasoconstriction of blood vessels resulting in an increase in blood pressure. ACE inhibitors such as enalapril prevent this effect. Enalapril has been shown to lower the death rate in systolic heart failure. Enalapril was the first member of the group known as the dicarboxylate-containing ACE inhibitors. Enalaprilat, the first dicarboxylate-containing ACE inhibitor, was developed partly to overcome these limitations of captopril. The sulfhydryl moiety was replaced by a carboxylate moiety, but additional modifications were required in its structure-based design to achieve a similar potency to captopril.