Valdes becomes the third lefty in the Cardinals' bullpen, joining Trever Miller and Brian Tallet. It's unclear exactly how he will be used, since he doesn't profile as a classic specialist, but with the ongoing struggles of the lefties already on the club, the Cards felt a move was necessary.
"My understanding is he's probably most suited for sort of a left-right-left scenario where he could see multiple hitters," general manager John Mozeliak said. "We'll try not to overexpose him and try to make him a long guy. We're just trying to make do and trying to work through our bullpen situation."
Valdes has thrived for Memphis since being moved to the bullpen. In 14 relief appearances spanning 16 1/3 innings, he has allowed six hits and one run, striking out 16 against one walk.
"His [Triple-A] manager and pitching coach have given him a good recommendation," manager Tony La Russa said. "That counts for a lot."
In additional adjustments, Memphis right-hander David Kopp was outrighted off the 40-man roster. Bryan Augenstein was activated from the 60-day disabled list and optioned to Triple-A as well. Augenstein will pitch in relief in Memphis. The Cardinals' 40-man roster is once again full after being at 39 players before Thursday.
Valdes, 33, signed with the Cardinals in the offseason after going 3-3 with a 4.91 ERA in 38 appearances for the Mets last season, striking out 56 in 58 2/3 innings. He was 5-2 with a 5.05 ERA in 21 games (seven starts) for Memphis this season and has done well since being removed from the rotation -- posting a 0.55 ERA and holding opponents to a .109 average in his 14 relief outings.
Valdes has been given uniform No. 37.