Flaherty was recalled from Triple-A Memphis and will start Tuesday against the Twins.
Flaherty is up to replace Adam Wainwright, who hit the disabled list with elbow inflammation. He could be up for an extended period, with Carlos Martinez (lat) also on the disabled list and without a return timetable. In two starts for the Cardinals this season, Flaherty has 11 strikeouts and five walks in 10 innings, allowing four runs on 10 hits.