Jeff Abraham says Carlin went into St. John's Health Center on Sunday afternoon, complaining of chest pain. Carlin died at 5:55 p.m. PDT, the Associated Press reported.
Carlin, who had a history of heart trouble, performed as recently as last weekend at the Orleans Casino and Hotel in Las Vegas.
"He was a genius and I will miss him dearly," Jack Burns, who was the other half of a comedy duo with Carlin in the early 1960s, told The Associated Press.
Carlin was best known for his routine "Seven Words You Can Never Say On Television," which appeared 1972's "Class Clown" album.
When Carlin uttered all seven at a show in Milwaukee in 1972, he was arrested for disturbing the peace, the AP reported. The comedy sketch prompted a landmark indecency case after WBAI-FM radio aired it in 1973.
The case was appealed to the U.S. Supreme Court where the justices ruled on a 5-to-4 vote that the sketch was "indecent but not obscene," giving the FCC broad leeway to determine what constituted indecency on the airwaves.
"So my name is a footnote in American legal history, which I'm perversely kind of proud of," Carlin said. "In the context of that era, it was daring."
"It just sounds like a very self-serving kind of word. I don't want to go around describing myself as a 'groundbreaker' or a 'difference-maker' because I'm not and I wasn't," he said. "But I contributed to people who were saying things that weren't supposed to be said." Watch Carlin's 7 dirty words routine »
Carlin, who was also an author, was slated to receive the 2008 Mark Twain Prize for American Humor in November.
"In his length career as a comedian, writer, and actor, George Carlin has not only made us laugh, but he makes us think," Stephen Schwarzman, Kennedy Center chairman, said in a statement. "His influence on the next generation of comics has been far-reaching."
In a typical wry response, Carlin said: "Thank you Mr. Twain. Have your people call my people."
Carlin hosted the first broadcast of "Saturday Night Live" in October 1975.
He played the character of Mr. Conductor on the PBS series "Shining Time Station" and starred in more than a dozen HBO specials. Carlin was also a regular on The Tonight Show.
He produced 23 comedy albums, 14 HBO specials, three books, a couple of TV shows and appeared in several movies, from his own comedy specials to "Bill and Ted's Excellent Adventure" in 1989 -- a testament to his range from cerebral satire and cultural commentary to downright silliness (and sometimes hitting all points in one stroke), the AP reported.
"Why do they lock gas station bathrooms?" he once mused. "Are they afraid someone will clean them?"He won four Grammy Awards, each for best spoken comedy album, and was nominated for five Emmy awards, according to the Associated Press.