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ST. LOUIS – A St. Louis heart transplant program has reached a significant milestone, 500 heart-only transplants.

The St. Louis Children’s and Washington University Heart Center says the 500th transplant began Wednesday and was completed Thursday morning. The surgery took 10 hours.

The center performed its first heart transplant in 1986, four months after a Denver 4-year-old became the world’s first successful pediatric heart transplant recipient. The St. Louis center now treats patients from across the country, averaging 15 to 20 heart transplants per year.