The cosmopolitan Heinrich Isaac adroitly adapted his compositional style to fit the liturgical and aesthetic norms of his surroundings, while always retaining his characteristic fluency. While serving the splendid Renaissance court of Medicean Florence, he wrote stylish French chansons, and contributed settings of the Mass Ordinary based on popular secular tunes. After Savonarola's coup ousted the regime, Isaac began (around 1497) a long tenure as Court Composer to the Holy Roman Emperor Maximilian I, and wrote idiomatic German Tenorlieder. For the Imperial chapel services Isaac produced a large number of Masses, based somewhat more decorously upon plainchant liturgical melodies. Most of these serve the observance of specific feasts; no fewer than four bear the title "Missa Paschale," or "Easter Mass."

The solemn High Mass of Easter according to the Imperial Rite of Passau had a specific set of designated plainchants. Isaac's four Paschal Masses—two for four voices, and one each for five and six voices—all use this heterogeneous but fixed group of chants as cantus firmus, generally quoting the proper plainchant in at least one voice at all times. In each Mass he provides a polyphonic setting of four movements only, as the Credo was not sung in the Imperial liturgy. In addition, Isaac composed according to local German practices of alternatim performance: phrases of his polyphonic setting alternate with phrases of simple choral plainchant. At times the chant itself could be replaced by improvisation on the organ; a contemporary woodcut shows the Imperial Chapel singing Mass, with the legendary organist Paul Hofhaimer at his instrument.

Within the strictures of this Imperial liturgy and local style, Isaac provides in these four Masses a dazzling array of techniques for elaborating his chant melodies. His most common approach is to place the chant melody in either the upper voice or the tenor, with long note values contrasted to more rapid counterpoint in the other voices. A good deal of the four-voiced Missa Paschale II adopts this technique. Each section of the Kyrie from the other four-voiced Missa I, on the other hand, dramatically begins with long-note imitation in all voices of the plainchant, and gradually devolves into Ockeghem-like rhythmic drive to the final cadence. The Domine Deus from this same Mass opens with a long and sparse duo texture, reserving the full four voices for the divine Name Jesu Christe. The five-voiced Mass often deploys quasi-canonic procedures: its Kyrie transposes the chant between voices, the Gloria gives the chant in canon in the three lowest voices beneath a florid upper pair, and the Sanctus even mimics a "mensuration canon" where the tune is given in different voices in different meters. The six-voiced Easter Mass passes the chant between the upper voice and tenor; it also explores a number of different vocal textures, from imitation to plain homophony, with antiphonal effects and an archaic Fauxbourdon in the Sanctus.

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