Heyward hasn't played since May 19, which was part of a three-game stretch where he attempted to return from his shoulder injury. It didn't go well and he had to go back to the bench due to the pain. They finally gained a little bit of sense and put him on the disabled list to prevent any further damage.
It seemed pretty certain Heyward needed a DL stint considering it was an injury that had bugged him since Spring Training without getting any better. I'm no doctor, but assuming an injury will get better in a couple days after dealing with it for over a month isn't exactly smart, especially with a shoulder injury. However, the team doctors and Heyward continued to do the opposite of what they should do and he continued playing with little effect, as well as prolonging the time it would take for him to recover.
Nate McLouth, who left Sunday's game due to an oblique injury, will be evaluated Monday.