Angiotensin converting enzyme (ACE) is a key enzyme in the regulation of blood pressure and fluid balance, and is a target for many drugs used to treat hypertension and heart failure. Synonyms for ACE include peptidyl-dipeptidase A, dipeptidyl carboxypeptidase, and kininase II. These names refer to different aspects of the enzyme's function, such as its ability to cleave peptides and its role in the metabolism of bradykinin, a vasoactive peptide. ACE inhibitors, such as lisinopril and captopril, are among the most widely prescribed drugs for the treatment of hypertension and heart failure, and work by blocking the action of ACE.