Heeney sent a scare through the Swans camp after suffering a lower back issue during the club's eventual 16-point loss to Adelaide at the SCG.
The Swans vice-captain had come off second-best after a contest for the ball with Crows forward Riley Thilthorpe.
But the 30-year-old work-horse, who has only missed one game this season, was given the all-clear minutes later and finished with 29 disposals, four clearances and 16 contested possessions.
"He was sore for the back part of that game," Cox said.
"The thing with Isaac though, as soon as he rocks up, he wants to play and play all the way through.
"You want him to play ahead of the ball, as well as to try and kick you a score, and then around the middle of the ground.
"When we need some ascendancy, he's probably the one we always look to. He's carried a fair load this year."
But the Swans are set to be without veteran defender Harry Cunningham, who was concussed after a high tackle from Adelaide key forward Darcy Fogarty in the second quarter.
Suffering back-to-back defeats for the first time this season, Cox lamented a missed opportunity for the Swans to tighten their grip on second place.
Adelaide can finish round 19 as high as third and are just four points behind Sydney.
The Swans had capitulated after clawing back a game-high 27-point lead.
"A side (Adelaide) that had dominance for a half, first and last quarter and took massive advantage in it," Cox said.
"When you play the number one pressure team and contested ball team, they did it for longer.
"We need to do it for longer. At the minute, we're not doing that."
Losing their first SCG match of the campaign, Sydney will lick their wounds ahead of next week's derby clash against a red-hot GWS outfit.
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