I know it's techcally not a heist movie but if you a real fan of heist film, you must watch Le Trou (1960). It's one of my absolute favorite movie with unforgetable ending.
The Hole (French: Le Trou) is a 1960 French crime film directed by Jacques Becker. It is an adaptation of José Giovanni's 1957 book The Break. It was called The Night Watch when first released in the United States, but is released under its French title today. The film is based on a true event concerning five prison inmates in La Santé Prison in France in 1947. Director Becker, who died just weeks after shooting had wrapped, used mostly non-actors for the film's main roles, including one man (Jean Keraudy) who was actually involved in the 1947 escape attempt, and who introduces the film. It was entered into the 1960 Cannes Film Festival.
The black and white cinematography is by Ghislain Cloquet (Mickey One, Au hasard Balthazar, Tess).
The scene where three different characters take turns breaking through the concrete floor of their cell is filmed in a single, nearly four minute long, shot.
There is no musical score except under the end credits.
The film has no opening credits.
-Wikipedia