The Bluebirds received a huge boost on the eve of their season opener in the Championship with the news their transfer embargo has been lifted by the Football League.
Heaton, Drinkwater and Koumas have now been registered and are eligible to feature against the Blades in what is the Bluebirds' first competitive encounter since their play-off final defeat to Blackpool.
Goalkeeper Heaton competes with David Marshall for the number one jersey while Drinkwater will battle for a starting berth in midfield, but Koumas is not 100% match ready and is likely to find himself being introduced from the bench.
Manager Dave Jones will be without midfielder Stephen McPhail who is recovering from a knee operation.
However Jones is hopeful of having striker Jay Bothroyd available after a slight hamstring problem.
Kick-off at the Cardiff City Stadium is at 12.35pm.