This peptide is angiontensin II (Ang II) with Isoleucine universally labeled with 13C and 15N. The octapeptide angiotensin II (Ang II) exerts a wide range of effects on the cardiovascular system. It is also implicated in the regulation of cell proliferation, fibrosis and apoptosis. Ang II is formed through cleavage of Ang I by the 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.