“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.” A doctor attending the play immediately came backstage to treat the actor, and Mitchell was quickly rushed to the hospital. The play has resumed performances with a replacement angel.