Bell, who was a major league ump for 21 years, died at a Youngstown hospital at age 48, the Youngstown Vindicator reported.
He had open-heart surgery in 1999.
Fellow umpire and close friend John Hirschbeck told WFMJ-TV, Youngstown, Bell was one of his "dearest friends."
"We worked together for 11 years. He was like to a son to me, my wife Denise, very dear friend. It's devastating. Wally was one of the first to call me and congratulate me on working the World Series," Hirschbeck said.
Bell leaves behind two children, Lindsey and Jason.