Iowa manager Pat Listach said afterward that Hart suffered a concussion, but he didn't believe it was serious.
"He's OK. He's a tough kid," Listach said. "We'll see what [the doctors] say."
Hart entered Wednesday with a 3.81 ERA in six starts with Iowa this season. Acquired from the Orioles in December, 2006, Hart rose to the big leagues by the end of last season and had a 0.82 ERA in eight relief appearances in September, earning his way onto Chicago's post-season roster.
This season, Hart had a 6.62 ERA in 17 2/3 innings with Chicago.
Another Iowa pitcher, right-hander Jesse Estrada, was struck with a comeback line drive in early May while pitching for Class AA Tennessee in a game at Chattanooga.
Broussard Goes Yard
Veteran 1B/OF Ben Broussard, whom the Cubs signed last week, hit a towering home run out of Principal Park in the Cubs' 5-3 win over the Zephyrs Wednesday.
The recently acquired left-handed hitter sent a 1-2 offering from Zephyrs pitcher Jose Santiago at least 400 feet over the centerfield wall in the eighth inning. Broussard recorded his first hit with Iowa earlier in the game, and finished 2-for-3 with a walk.
Listach said it was just a matter of time before Broussard started to heat up.
"We'll try to play him in left field while Soriano is still out in case they need another piece to the puzzle in Chicago," he said.