The Indians also activated pitcher Fausto Carmona after he spent two months on the disabled list and demoted struggling left-hander Aaron Laffey to Triple-A Buffalo. In addition, Cleveland purchased infielder Andy Gonzalez's contract from Buffalo.
Carmona was 4-2 with a 3.10 ERA when he went on the disabled list May 24 with a left hip strain. He made two minor league rehab starts this month and was scheduled to start Saturday night against Minnesota.
Laffey was 5-7 with a 4.23 ERA in 16 starts with the Indians. He allowed eight runs and 12 hits in four-plus innings in his last start Wednesday against the Los Angeles Angels.
"It's a natural part of the development process," Cleveland general manager Mark Shapiro said of Laffey's demotion. "He's a guy we still believe strongly in."
Laffey's departure means right-hander Matt Ginter will remain in the rotation. Ginter was called up from Buffalo on July 12. He is 1-1 with a 2.45 ERA in two starts.
The 26-year-old Reyes has split this season between the Cardinals' bullpen and the starting rotation at Triple-A Memphis. The right-hander was on St. Louis' opening day roster and went 2-1 with a save in 10 relief appearances. He was placed on the disabled list in June with a sprained right elbow.
"He's had mixed success at the major league level," Shapiro said. "He struggled this year. It was an opportunity to acquire someone who has a lot of upside, potential and good stuff. Hopefully, we acquired him at the right time."
Shapiro said Reyes will get a spot in the Triple-A rotation, and he's expected to join the Indians at some point this season.
Reyes likely will compete for a spot in Cleveland's rotation next spring.
At Memphis, Reyes was 2-3 with a 3.25 ERA in 11 starts.
"I don't think there's anything objectionable to getting a fresh start," Cardinals manager Tony La Russa said before a game against the New York Mets.
La Russa dismissed any suggestion that a rift developed between Reyes and the Cardinals coaching staff, in particular pitching coach Dave Duncan, over his style of pitching. Reyes has had problems with a four-seam fastball that tends to stay up in the strike zone.
Reyes also struggled living up to the enormous expectations that came with holding Detroit to four hits in eight-plus innings in the Series opener two years ago. St. Louis went on to beat the Tigers in five games to win the title.
"We brought him up. We were trying to work in his best interest," La Russa said. "The thing we kept looking at was the stuff he had to do he wasn't quite doing."
The 24-year-old Perdomo has made nine appearances at Double-A Akron, after beginning the season at Class-A Kinston. La Russa wasn't sure where the Cardinals would send him.
It was the second trade of the day for the Indians, who earlier dealt third baseman Casey Blake to the Los Angeles Dodgers for two minor leaguers: switch-hitting catcher Carlos Santana and pitcher Jonathan Meloan.