Angiotensin-converting enzyme inhibitor is an antihypertensive drug. Literally, angiotensin-converting enzyme inhibitor is an agent that inhibits angiotensin-converting enzyme. Angiotensin-converting enzyme is an enzyme secreted by the body, and its main function is to constrict blood vessels and raise blood pressure, so angiotensin-converting enzyme inhibitors can play a role in lowering blood pressure. Angiotensin-converting enzyme inhibitors are the most commonly used antihypertensive drugs in clinical practice, and can be used not only to lower blood pressure in hypertensive patients with combined coronary artery disease and diabetes, but also to improve the prognosis of such patients. When using angiotensin-converting enzyme inhibitors, it is important to know not only the indications but also the contraindications, because the use of these drugs in patients with contraindications may lead to aggravation of their condition, for example, patients with bilateral renal artery stenosis or patients with hyperkalemia should not use these agents. The specific use of angiotensin-converting enzyme inhibitors should be discussed with a medical professional.