The octapeptide angiotensin II exerts a wide range of effects on the cardioVascular system. It is also implicated in the regulation of cell proliferation, fibrosis and apoptosis. Angiotensin II is formed by cleavage of angiotensin I by angiotensin-converting enzyme (ACE) or chymases. Human heart chymase, a chymotrypsin-like serine proteinase, hydrolyzes the Phe8-His9 bond to yield the octapeptide hormone angiotensin II and His-Leu.