All the diamonds in the film are real.
To achieve the horrified reaction of Mira when firing the gun, the director intentionally scared the actress.
The music during the End credits is the exact same minuet by Mozart used during the robbery but done with a reggae beat.
Several years earlier, Marissa Stott worked with Campbell Cooley on Shortland Street (1992) playing a character who didn't speak. Her character in The Heist also never speaks.
The lead character was named Mira because of its similarity to Mirror; an allusion to all the mirror-relationships in the story (and all the reflective surfaces in the diamond boutique).