John Ritter, 54, whose portrayal of the bumbling but lovable Jack Tripper helped make the madcap comedy series "Three's Company" a smash hit in the 1970s, died of a heart ailment Sept. 11 at a Burbank, Calif., hospital. He fell ill on the set of his new sitcom, ABC's "8 Simple Rules . . . For Dating My Teenage Daughter," a hit show that had became the actor's big television comeback.

He succumbed to a dissection of the aorta, a break in the main artery that carries blood from the heart, his publicist said. Doctors described it as a rare medical disaster that can strike without warning.

Mr. Ritter, a Southern California native, came to prominence for his role in "Three's Company" and had appeared in more than 25 television movies and a number of films and on Broadway. He made his successful return to sitcom acting last year with "8 Simple Rules." The show was scheduled to begin its second season Sept. 23.

Mr. Ritter was the youngest son of Western film star and country musician Tex Ritter and actress Dorothy Fay. He graduated from Hollywood High School and earned a degree in drama from the University of Southern California. His first steady job was his role as a minister in television's "The Waltons."

With "Three's Company," his career took off. His performances included 1996's Oscar-winning drama "Sling Blade" and a Broadway run in Neil Simon's "The Dinner Party." He received an Emmy and other awards for his "Three's Company" role and was honored by the Los Angeles Music Center in June with a lifetime achievement award.

"Three's Company," about a bachelor sharing an apartment with two attractive women, Suzanne Somers and Joyce DeWitt, was considered racy during its run from 1977 to 1984. Mr. Ritter worried about falling into a typecasting trap after the show ended.

"I would get scripts about 'a young swinging bachelor on the make,' and I said, 'No, I've done that,' " he told the Associated Press in a 1992 interview. "Or they'd say, 'You're living alone and. . . .'

"What I was looking for in my time off was something a little bit different, a little serious, or funny in a different way."

He later starred in the television series "Hooperman" and the early 1990s political comedy "Hearts Afire." He received two Emmy nominations for his PBS role as the voice of "Clifford the Big Red Dog" on the animated series.

His TV movie appearances included "Unnatural Causes," Stephen King's "It" and "Chance of a Lifetime."

Mr. Ritter won popularity among independent film directors in recent years and appeared in films that included "Tadpole" in 2002 and the new feature "Manhood." He appears alongside Billy Bob Thornton in the scheduled November release from Miramax "Bad Santa."

He was married from 1977 to 1996 to Nancy Morgan.

Survivors include his wife of four years, actress Amy Yasbeck, and four children.

John Ritter, shown with co-stars Joyce DeWitt and Suzanne Summers, starred as Jack Tripper in "Three's Company" from 1977 to 1984.