Heppner, a regular performer at the Metropolitan Opera, Royal Opera, and other top houses, will be making his Opera Colorado debut.
Also added to the roster of singers was tenor Garrett Sorenson, an alumnus of the Metropolitan Opera's Lindemann Young Artist Development program.
Singers previously scheduled to appear include mezzo-soprano Judith Christin, soprano Kristen Clayton, soprano Ren_e Fleming, tenor Julian Gavin, soprano Cynthia Lawrence, bass-baritone James Morris, baritone Robert Orth, soprano Emily Pulley, mezzo-soprano Marcia Ragonetti, baritone Charles Taylor, bass-baritone Hao Jian Tian, bass-baritone Stephen West, mezzo-soprano Theodora Hanslowe, and baritone Yalun Zhang.
Stephen Lord, music director of the Opera Theatre of St. Louis and Boston Lyric Opera will conduct. Composer Jake Heggie will appear as a pianist, accompanying Clayton in the world premiere of his and playwright Terrence McNally's "mini-opera" At the Statue of Venus.