That wasn't a doctor on "Late Show" after all who was introduced by David Letterman last February as one of the heart specialists who saved Dave's life during quintuple bypass surgery. He was an actor playing a doctor. The "cardiac cowboy" introduced by Dave was meant to be the real-life Dr. O. Wayne Isom, reports the Chicago Tribune. But the good doctor was really on a plane headed toward Jamaica. So producers shot a few close-ups of him the day before Letterman took to the stage, introduced a team of doctors, and, with moist eyes, announced: "It was five weeks ago today that these men and women right here saved my life." (Isom's close-ups were edited into the program.) The show, marking Dave's return to the air after his health problem, was a ratings winner. But it was staged dramatic reading, not a true-life presentation. "This was never a big secret or cover-up," the CBS program's executive producer Rob Burnett tells today's New York Post. "We told anybody who wanted to know that Dr. Isom was not there and he would be cut into the show later."