Gregory Mitchell, the 52-year-old actor who suffered a heart attack onstage at the Kennedy Center on Thursday, remained hospitalized in serious condition yesterday.

Mitchell was appearing as an angel in a play starring the legendary dancer Mikhail Baryshnikov. The two were performing a scene in which Mitchell's character was trying to rescue Baryshnikov's character, a retired sailor who has thrown himself into the sea. Mitchell appeared to be breathing heavily and then fell backward. He was wearing two wings and made a crunching sound when he fell, according to a member of the audience.

Once it was clear Mitchell's fall was not part of the play, officials at the Terrace Theater brought down the curtain and asked if there was a doctor in the audience. One responded immediately and tended to Mitchell backstage.

The capacity crowd of 500 sat quietly until being directed to leave, said an audience member.

"He was rushed to George Washington University Hospital where he is in serious condition. We are waiting and praying for his recovery," said Christina Sterner, managing director of the Baryshnikov Dance Foundation, which produced the play, "Forbidden Christmas, or the Doctor and the Patient."

This was the first time in the history of the Kennedy Center that an actor had collapsed onstage, said spokeswoman Tiki Davies.

The show will go on with Luis Perez replacing Mitchell. Perez created the role of the angel earlier this year and is the production's choreographer. Because of the show's short run -- it is scheduled to close tomorrow after six performances -- there was no understudy for Mitchell.

Mitchell was born in Brooklyn, N.Y., and graduated from Juilliard. In recent years, he has appeared on Broadway in the revivals of "Man of La Mancha," and "Chicago" as well as the original musicals "Steel Pier," "Merlin" and "Kiss of the Spider Woman." A frequent actor on television soap operas and dramas, such as "Law & Order," he also appeared in the Oscar-winning film version of "Chicago."

Mitchell is scheduled to perform next year in a play based on dancer Chita Rivera's life.

The play is a rare opportunity to see Baryshnikov as a stage actor. In 1989 he earned a Tony nomination for his acting role in Steven Berkoff's "Metamorphosis." "Forbidden Christmas," written by Rezo Gabriadze, is set in a small town in Soviet Georgia in the 1950s, where the observation of Christmas has been forbidden. On that holiday, however, Baryshnikov's character, who believes he is a car, and his doctor become entangled in matters of madness and the meaning of life.

Actor Gregory Mitchell.