It's the second major league start for the 24-year-old Hess. Baltimore optioned left-hander Donnie Hart to Norfolk to make room on the roster.
Hess made his big league debut on May 12, when he held Tampa Bay to three runs in six innings at Camden Yards in the opener of a doubleheader against the Rays.
Hart was 0-0 with a 1.93 ERA in four games.
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