Quinapril-d is intended for use as an internal standard for the quantification of quinapril by GC- or LC-MS. Quinapril is a prodrug form of the angiotensin converting enzyme (ACE) inhibitor quinaprilat. In vivo, quinapril (3 mg/kg) reduces mean arterial pressure in renal hypertensive and spontaneously hypertensive rats. It inhibits angiotensin I-induced pressor responses in normotensive rats and dogs. Quinapril (10-200 mg/kg) prevents left ventricular heart failure in CHF 14.6 cardiomyopathic hamsters. Formulations containing quinapril have been used in the treatment of hypertension, heart failure, and diabetic nephropathy.