Hart was optioned to Triple-A Norfolk on Wednesday.
Mark Trumbo (ribs) returned from the 10-day DL in a corresponding move and Hart was the roster casualty as a result. The left-handed reliever has put together some solid numbers since being called up in June, posting a 2.00 ERA while mainly serving as a middle reliever in low-leverage situations. He'll serve as organizational depth for now, but could provide a viable bullpen option if need be.