The present invention relates to 4'-[(1R)-1-[[(6,7-dichloro-3-oxo-2,3-dihydro-4H-1,4-benzoxazin- 4-yl)acetyl](methyl)amino]-2-(4-morpholinyl)ethyl]-4-biphenylcarboxylic acid and its pharmaceutically acceptable salts, pharmaceutical compositions containing them, and their use as antagonists of urotensin II.