ACE inhibitors are thought to modify the endothelium in a number of ways. Quinapril is an effective and well-tolerated ACE-I for the treatment of patients with hypertension and congestive heart failure. Quinapril produces favourable haemodynamic changes and improves ventricular and endothelial function in patients with various cardiovascular disorders. These effects are mediated through the binding of quinaprilat to both tissue and plasma-ACE.