A Las Vegas magician and wannabe gangster Buddy "Aces" Israel (Jeremy Piven) is hiding out in a Lake Tahoe hotel penthouse with his entourage. His agent, lawyer Morris Mecklen (Curtis Armstrong), discusses a potential immunity deal with FBI Deputy Director Stanley Locke (Andy Garcia). Agents Richard Messner (Ryan Reynolds) and Donald Carruthers (Ray Liotta) learn that ailing Las Vegas mob boss Primo Sparazza (Joseph Ruskin) has issued a bounty on Israel worth $1 million; a mysterious assassin known only as The Swede has sworn that he will bring Israel's heart to Sparazza. A number of assassins also seek the reward, including Lazlo Soot (Tommy Flanagan), who specializes in disguises and impersonations; Sharice Watters (Taraji P. Henson) and Georgia Sykes (Alicia Keys), two hitwomen hired by Sparazza's underboss, Victor "Buzz" Padiche (David Proval); Pasquale Acosta (Nestor Carbonell), a calm torture expert and mercenary; and the psychotic neo-Nazi Tremor brothers, Darwin (Chris Pine), Jeeves (Kevin Durand), and Lester (Maury Sterling).
Locke dispatches Messner and Carruthers to take Israel into custody when the deal is struck. Meanwhile, a team of Las Vegas bail bondsmen, Jack Dupree (Ben Affleck) and his partners, "Pistol" Pete Deeks (Peter Berg) and Hollis Elmore (Martin Henderson), has been hired by the sleazy lawyer who posted Israel's bail, Rupert "Rip" Reed (Jason Bateman), to bring him into custody. The bondsmen are gunned down by the Tremors, but Elmore survives. Messner is dispatched to the murder scene while Carruthers proceeds to Israel. At the same time, each of the assassins gain access to the hotel in their own various ways.
Carruthers encounters Acosta, disguised as a security officer, in an elevator at the hotel. Carruthers senses something is wrong and both are mortally wounded in a gunfight. Meanwhile, Soot gains access to the penthouse by posing as one of Israel's henchmen. Israel's second-in-command, Sir Ivy (Common), learns that Israel agreed to inform upon Ivy as part of the plea deal and attempts to kill him, but Israel injures Ivy by throwing a playing card at his eye, causing him to shoot his gun wildly around the room. The hotel security team hear the shots and restrain Ivy in riot cuffs in the hallway. Georgia finds Carruthers and Acosta, both riddled with bullets and bleeding to death, in the elevator, but assumes Acosta is Soot. In Los Angeles Locke abruptly withdraws from the deal with Israel and orders that Messner and Carruthers are not told. The Tremor brothers reach the penthouse floor, where they engage in a shootout with the security team and Ivy, who manages to kill Jeeves and Lester. Israel, learning of the FBI's new position, attempts suicide by gunshot but passes out before he can.
Messner arrives at the hotel and sets up a position around Georgia's elevator. Sharice provides cover from another high-rise hotel with a Barrett M82 anti-materiel rifle, outgunning the FBI agents. Acosta, still alive, shoots Georgia, but is shot by Carruthers. Sharice, thinking Georgia is dead, refuses to escape and keeps shooting at the FBI team. Georgia escapes to the penthouse where she stops Darwin Tremor before he can kill Ivy. Darwin Tremor escapes by posing as an FBI agent in stolen clothes, and Messner, distraught over the death of Carruthers, stops Ivy and Georgia on the stairwell, but decides to let them escape. Sharice, after seeing the pair alive and free through her rifle scope, is gunned down by the FBI from behind.
Locke and a team of FBI agents descend on the penthouse and take Israel to the hospital, while Soot escapes by dressing as a member of hotel security. Acosta, carted away on a gurney, is also shown to be alive. Darwin Tremor nearly escapes, but is gunned down by Hollis Elmore on the casino's parking garage roof.
Messner arrives at the hospital and learns the truth about the day's events from Locke at gunpoint. It transpires that the mysterious Swede is actually a prominent heart surgeon from the University of Stockholm and that Soot was hired by Sparazza to get Israel's heart so it could be transplanted into the body of Sparazza. Sparazza is further revealed to be Freeman Heller (Mike Falkow), an FBI agent who went undercover and was thought to have been killed by the mob. The FBI had attempted to kill Heller, after they thought his assignment had blurred the lines between being a mobster or an FBI agent. But Heller miraculously survived and ended up taking on the role as Sparazza full-time after his mind snapped. The mobster has agreed to expose the mob's operations in exchange for Israel's heart as he is in fact Sparazza's son, and thus, the most compatible donor.
Messner, furious over the unnecessary deaths, especially Carruthers', protests and is ordered by Locke to either resign on the spot or return to Washington, D.C., and forget about the case. Realizing that the FBI will never admit what they did, he walks into the emergency room, locks the door and pulls the plug on both men. He then lays his gun and badge on the floor while Locke and his men desperately try to break in.

Question: For what did Heller agree to expose the mob's operations?
Answer: Israel's heart
Alternative answer: He wanted Israel's heart as a transplant.