Used primarily in the treatment of hypertension and heart failure. It works by inhibiting the angiotensin-converting enzyme (ACE), which reduces the production of angiotensin II—a substance that constricts blood vessels and increases blood pressure. By blocking this enzyme, it helps blood vessels relax and widen, improving blood flow and lowering blood pressure. This action also reduces the workload on the heart, making it beneficial for patients with left ventricular dysfunction following myocardial infarction. Often administered in the form of its prodrug, quinapril, which is converted to quinaprilat in the body for active effect.