City Slickers

In New York City, Mitch Robbins, Phil Berquist and Ed Furillo are in midlife crises. Mitch has just turned 39, Phil is trapped in a 12-year loveless marriage to his overbearing wife, Arlene, and Ed is a successful sporting goods salesman and playboy who has recently married an underwear model but is struggling with monogamy and the pressure of having children. Ed's suggestions for youthful adventures do little to placate them, and Phil's marriage soon falls apart due to an affair with one of his co-workers.
At Mitch's birthday party, Phil and Ed present a gift of a two-week cattle drive from New Mexico to Colorado. Despite Mitch's plans to go to Florida with his wife Barbara to visit her parents, Barbara persuades him to instead go with his friends and find some purpose before he contemplates adultery or suicide. In New Mexico, Mitch, Phil and Ed meet the ranch owner, Clay Stone, and their fellow drivers. Mitch develops a rivalry with the ranch's professional cowboys, Jeff and T.R., when they drunkenly proposition one of the drivers, Bonnie. The standoff is stopped by the trail boss, Curly, who inadvertently humiliates Mitch in front of his friends.
During the drive, as Mitch, Phil and Ed begin to change their outlook on life, Mitch accidentally causes a stampede which wrecks most of the camp. In retribution, Curly orders him to help gather the lost cows, but over time, the two develop a bond when Mitch learns that Curly, despite his tough exterior, is actually a very wise man. Curly advises Mitch to discover the "one thing" in his life which is the most important to him, which will solve all of his problems. Along the way, Mitch helps deliver a calf from a dying cow, which Curly kills out of mercy. Mitch adopts the calf and names him Norman.
Curly suddenly dies of a heart attack, leaving the drive under Jeff and T.R.. Trouble begins when the cook, Cookie, gets drunk and accidentally destroys their food supply, and Jeff and T.R. intoxicate themselves with Cookie's hidden stash. A fight ensues when they threaten Norman and assault Mitch, leading Phil to lash out at them and unleash a lifetime of stress on them at gunpoint. Jeff and T.R. abandon them to avoid reprisals from Clay Stone. Though the remaining drivers consider leaving the herd to seek out civilisation, Phil and Ed remain behind to finish the drive alone. Mitch has a change of heart and joins them while the others continue to Colorado.
After braving a heavy storm, they finally manage to drive the herd to Colorado, but Norman gets stuck in the river. Mitch saves him but they are both swept away with the current. Phil and Ed only barely manage to save them both and finally overcome their crises while resting on the bank. They reach Clay Stone's ranch in Colorado shortly afterwards. Clay Stone offers to reimburse them for their troubles, but reveals that he is selling the herd to a meat company. Having changed their outlook on life, Mitch, Phil and Ed decide to rebuild their lives, and Mitch purchases Norman from Clay Stone to save him from slaughter.
Mitch returns with Phil and Ed a happier man, and reunites with his family. Phil enters a relationship with Bonnie, and Ed becomes open to the idea of having children.

Question: How does Curly suddenly die?
Answer: heart attack