John van 't Schip's new-look side continues to take shape with the arrival of the promising three-cap Socceroo
Widespread reports emerged last season that out-of-contract midfielder Mooy would leave Western Sydney Wanderers at the end of the campaign and was tipped to swap red and black hoops for red and white stripes.
That free transfer has now been formally announced by Heart, who on Wednesday announced the capture of the 23-year-old on a two-year deal.
"Everyone who follows the A-League knows of Aaron's quality," Heart coach John van't Schip said in a statement.
"For us he can be a player who can dictate the style of football we want to play.
"He is one of the best young Australian players so we are delighted to have captured his signature. It shows the club's ambition to win trophies and play football a certain way."
Earlier this week Heart announced the signing of Jacob Melling from Adelaide United and the impending arrival of Connor Chapman and James Brown from the Newcastle Jets.