Two actors that Mann and co. had no trouble registering as the stars, Al Pacino and Robert De Niro. According to a New York Times article was published in July 1995 a few months before the release of “Heat”, the two had wanted to make a movie together for a while. When De Niro signed the contract after reading Mann’s script, Pacino quickly said yes. Producer Art Linson succinctly sums it up: “Great material attracts great actors. That’s what happened here. We gave the script in advance to Bob. After Bob, Al became interested. It’s the flow.”
In that article, Mann notes that Neil McCauley (De Niro) is a “highly organized killer.” On the other hand, Lieutenant Vincent Hanna is “not at all a sociopath killer but extremely dysfunctional, who invests his emotions and intuition in crime fighting.” Both have roles that match their strengths. De Niro, famously quiet, plays the cooler character, while the more pompous Pacino plays the explosive character.
The casting of two Hollywood legends gave “Heat” a marketing advantage; two movie star legends not only appear together but also confront each other. However, the casting of actors is also very important for the content of the film. Vincent Hanna and Neil McCauley are both main characters, so the actors can’t overshadow each other. If the movie only featured either Pacino or De Niro, there would be a power imbalance and the similarities between Hanna and McCauley wouldn’t resonate as much. The pair played such roles in “The Godfather Part II,” so it’s no surprise that they pull off the same trick in “Heat.”
https://www.slashfilm.com/938074/the-casting-process-for-heat-was-too-important-to-cut-short/ The molding process for heat is too important to truncate