Boyer is expected to be at Busch Stadium and available to pitch for Tuesday's 7:15 p.m. CT game against the Mets. The Cardinals will demote a position player to make room for him. That will likely be David Freese, though general manager John Mozeliak did not announce the corresponding move in a conference call on Monday afternoon.
Boyer, 27, got off to a rough start with Atlanta in 2009 and was designated for assignment. In three appearances, he allowed six runs in 1 1/3 innings. That follows a major second-half fade in '08 after an excellent beginning to the season.
If Boyer can repeat his first-half 2008 performance -- a 3.93 ERA, 45 strikeouts and 18 walks in 52 2/3 innings -- he'll be a significant asset to the Cardinals' bullpen. Of course, that's far from a guarantee.
"We do think this is a fresh start for him and one that will give him an opportunity to show what he's capable of doing," Mozeliak said.
For the next few days at least, the Cardinals will carry 13 pitchers. The club will use the time as an evaluation period to determine which seven relievers it wants to keep as the season goes on.
The St. Louis bullpen was stretched just about to its breaking point over its recent road trip. Cardinals starters totaled just 23 innings over the final five games of the trip, leaving the relief corps with a very heavy load. The club pondered adding a pitcher from the Minor Leagues for Sunday night's game in Chicago, but elected not to. That game was rained out, making it a moot point.
"This was an opportunity that presented itself when we noticed that he was designated," Mozeliak said. "This was not perpetuated because of what happened over the past few days."
In dealing Barton, the Cardinals part with an intriguing player but one who was expendable due to significant organizational depth. St. Louis selected Barton in the 2007 Rule 5 Draft and kept him on the roster for all of '08, but he did not crack the big league roster for '09.
He trailed four or five players on the depth chart, and was being pushed from behind by prospects such as Jon Jay and Daryl Jones. Thus, he's now headed to the Braves system, while St. Louis adds an interesting but uncertain arm.
"We're looking to add depth to an area that needed it," Mozeliak said. "Given some of the things that we had to face early on in this season, we see this as a positive."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.