Film critic Roger Ebert points out a key scene in the film in which Pacino and De Niro's characters agree to have coffee. It is a powerful moment, where the criminal and cop acknowledge and recognize each other's position. There is mutual respect, but also a surrendered acceptance that they will always been on two opposing sides.
But aside from the central conflict between these characters is the character Chris Shiherlis (played by Val Kilmer). Chris is a member of McCauley's (the part played by De Niro) crew, though also a thief, it appears that he is not deeply into the career as the others are. His presence serves as sort of an anchor for the audience to relate to -with McCauley and Hanna (Pacino) representing the two extreme opposites.
The basic plot of the movie revolves around McCauley and his crew of bank robbers. The group manages a successful heist. However, those willing to break the law can also be hard to control, and McCauley sees this firsthand when one of his crew, Waingro, shoots down a cop unneededly. This forces the rest of the team to kill the remaining guards in order to remove all witnesses. McCauley tries to kill Waingro, but the hot tempered thief escapes. To make matters worse, the crew find themselves being targeted by other groups for their score (starting with an ambush by their fence).
Meanwhile the LAPD assembles a special team lead by Vincent Hanna in order to track down and arrest McCauley. And while tracking down McCauley, Hanna realizes that they are far more formidable than expected. Meanwhile, Waingro makes a deal with a money launderer Van Zant and they target McCauley.
When the crew are attacked by Van Zant, McCauley becomes obsessed with revenge against Waingro, passing up plenty of chances to get away safely with his girlfriend. The movie ends with McCauley finally killing Waingro, but he too dies as he tries to escape from Hanna.
Aside from good direction and great acting, Heat benefits greatly from the life stories and advice of actual career criminals. The lead character McCauley is based on a real person named Neil McCauley, a former inmate in Alcatraz who later became a very active criminal who specialized in heists. The dialogue between Pacino and De Niro over coffee is inspired by a very similar event when Neil had coffee with Detective Chuck Anderson. It's an iconic moment in the film and their relationship throughout is big part of why so many people became big fans of the crime thriller. Thankfully we will get to see Deniro and Pacino work together again in the upcoming 'The Irishman' gangster movie directed by Martin Scorsese.
In many ways, the film is an imitation of life -the ending of the film, Hanna shooting down McCauley, is what happened to Neil. After stealing from an armored car's drop off (a grocery store), Neil and his crew try to drive away but are quickly blocked by the police. They try to fight their way through, but Neil and two of his crew die in the ensuing firefight (Neil actually manages to run away for a small distance before getting shot down). The fourth member of the crew actually managed to get away from the police but was arrested several days later. This is the last surviving meber of McCauley's crew (Val Kilmer's character is modeled after him).
The detective, Chuck Anderson, would later have a successful career outside of law enforcement -he became a television and film producer. In 2008, Anderson died at the age of 71.