Isaac, Heinrich(hīn`rĭkh ē`zäk), c.1450–1517, Flemish composer. Isaac, a prolific and versatile composer, traveled widely in Europe, serving at the courts of Lorenzo de' Medici and Emperor Maximilian I. Among his best-known works is the collection of 99 four-part settings of the proper chants of the mass known as Choralis Constantinus, a monumental collection of Gregorian liturgical music. He also wrote many motets, masses, hymns, and secular songs.
See A. Einstein, The Italian Madrigal (3 vol., 1949, repr. 1971).