A/an blocks the enzyme action that causes the blood vessels to contract.

An ACE inhibitor blocks the enzyme action that causes the blood vessels to contract.
Angiotensin II is a chemical that the body produces. This chemical narrows the blood vessels by causing the muscles around them to contract which leads to the increase in the blood pressure.ACE inhibitors decreases the production of this chemical (Angiotensin II) causing the blood blood vessel to dilate and the thus the blood pressure decreases.
ACE inhibitors are used in several cases including:1- The prevention of strokes2- The control of high pressure of blood (whether chronic or accurate)3- Treatment of heart failure and dysfunction of the left ventricular 4- The prevention and treatment of kidney deseases for people suffering from diabetes or hypertension5- Improving the surivavl chance in case of heart attacks