Last month Heppner made a sort of partial withdrawal from the Philadelphia Orchestra's gala concert and ball for the 150th anniversary of the city's Academy of Music, at which he and soprano Deborah Voigt were the featured guest artists. Heppner who had completed a seven-concert recital tour of his native British Columbia only six days earlier — did appear, but he sang only one of the arias he had originally planned, with Dongwon Shin (who has developed something of a specialty in last-minute substitutions) taking the others.

Heppner did successfully sing the title role in a concert performance of Giordano's Andrea Ch_nier in Puerto Rico last Saturday (February 3). His next scheduled appearances are also as Ch_nier, in an eight-performance run at the Metropolitan Opera in March and April.

Filling in for Heppner as Tristan in Montreal next week will be tenor John Treleaven, who has sung the role at the Netherlands Opera, the Liceu in Barcelona, the Bavarian State Opera in Munich, and the Lucerne Festival, among other venues.

Joining Treleaven will be soprano Christine Brewer as Isolde, mezzo Mihoko Fujimura as Brang‹ne, baritone Dietrich Henschel as Kurwenal and bass Philip Ens as King Marke. Nagano, the OSM will give two complete concert performances of the opera with this cast at Montreal's Salle Wilfrid-Pelletier: February 15 at 7 p.m. and February 18 at 2 p.m. More information and tickets are available at www.osm.ca.