The move is retroactive to Saturday. Heyward is hitting .253 with three homers and 17 RBIs.
In another transaction Monday before their game against Colorado, the Cubs traded outfielder Matt Szczur to San Diego for minor league right-hander Justin Hancock. Szczur was designated for assignment Saturday to make roster room for a fresh arm in an overworked bullpen, a difficult choice for the Cubs. He hit .211 with three RBIs for Chicago this season.
The Cubs also selected the contract of right-hander Dylan Floro from Triple-A Iowa. Floro was 1-0 with a 5.06 ERA in eight appearances with Iowa this season.
The 26-year-old Floro was signed to a minor league deal by Chicago in the offseason.
Hancock, also 26, was 0-2 with a 6.23 ERA in 10 relief appearances for Double-A San Antonio.