The Nationals recalled Herz from Triple-A Rochester on Tuesday, Bobby Blanco of MASNSports.com reports.
Herz is set to make his major-league debut Tuesday as he makes a start against the Mets in place of Trevor Williams (elbow), who was placed on the injured list. The left-hander has posted a 3.75 ERA and 42:29 K:BB over 36 innings covering nine starts for Rochester this season. Herz boasts a 33.6 percent strikeout rate during his time in the minors, but he's also generated an elevated 15.3 percent walk rate.