Hartman underwent Tommy John surgery Wednesday, Jason Mackey of the Pittsburgh Post-Gazette reports.
Hartman was the Pirates' fourth-round pick during the 2020 first-year player draft, but he'll have a lengthy recovery process before making his minor-league debut. He's a pure reliever with a fastball that can reach 97 mph, but it's not yet clear what his velocity can be once he returns from surgery. He could make his first appearance in the minors at some point in 2022.