You can read them in the list below, according to zimbio.com!
1. Heat was shot entirely on location. It was filmed in 65 locations in and around Los Angeles.
2. De Niro and Pacino were Mann’s first choices for the roles of Neil McCauley and Vincent Hanna (the character based on Adamson).
3. Michael Mann wrote Heat in 1979, and eventually turned the script into a TV pilot called L.A. Takedown that aired in 1989. Creative differences pushed Mann away, however, and the show was cancelled.
4. Mann has said McCauley’s gray suits were designed to help him blend into a crowd and not draw attention to himself.
5. Mann never wanted to direct Heat, offering it to Walter Hill in the ’80s, who refused.
6. Chicago police officer-turned-actor Dennis Farina was a consultant on the film. He and Mann worked together on Crime Story years earlier.
7. Heat is based on real-life criminal Neil McCauley and the cop who nailed him, Detective Chuck Adamson, in 1964. Many of the film’s heist moments are taken from McCauley’s life of crime, including the armored car robbery and the diamond drill bit heist. McCauley and Adamson also met for coffee in real life and the conversation they had is the one you see in the film.
8. The coffee shop scene: De Niro suggested not rehearsing so the unfamiliarity would bleed into the scene. Mann agreed. The decision also fostered improvisation between the two famous actors. Mann used two cameras simultaneously so the conversation would be more fluid. The scene was shot at Kate Mantilini (now closed) in Beverly Hills.
9. Mann opted to use real audio for the robbery shootout as opposed to dubbing in post-production. The live sound design is as real as it gets and the scene has gone down as one of the best of its kind, if not the best.
10. Keanu Reeves was originally signed to play Chris Shiherlis, but Mann wanted Val Kilmer and Reeves lost the role when Kilmer’s Batman Forever schedule opened up. He filmed both movies at the same time.
11. The scene of McCauley standing against a window and watching the ocean (above) is inspired by the painting Pacific by Alex Colville.
12. Mann, De Niro, Kilmer, and Tom Sizemore (who plays Michael Cheritto) traveled to Folsom State Prison before filming to interview inmates and research their characters.
13. Danny Trejo was hired for the role of “Trejo” in the film, but he also helped as a crime consultant. Both he and Bunker had served time for armed robbery.
14. In an early draft of the script, Vincent Hanna had a cocaine habit, which explains his bombastic outbursts, according to Pacino.
15. The character of Nate, played by Jon Voight, is based on real-life criminal Edward Bunker, who died in 2005. Bunker had previously starred in another famous ’90s heist film: Reservoir Dogs. He plays Mr. Blue. Voight initially turned the role down, but Mann always wanted to work with him and convinced him to do it. Bunker was also a consultant on the film.
16. Pacino improvised the line: “…Because she’s got a GREAT ASS!” Hank Azaria, who shares the scene, was surprised by the reading and his reaction is genuine.