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Ritter, who would have been 55 on Wednesday, found fame in the 1970s as Jack in Three’s Company, about two women and a man sharing one apartment.

He collapsed while on the set of 8 Simple Rules and was taken to a nearby hospital in Burbank, California.

But doctors were unable to save him, and he died from a previously undetected heart problem.

Ritter was nominated for best actor at the prestigious Emmy TV awards three times for the Three’s Company, and won once.

He has recently seen a resurgence in his TV career, starring as a dad struggling to cope with feisty daughters in the ABC comedy 8 Simple Rules..., which is shown on the Disney channel in the UK.

TV guest roles included The Love Boat, Buffy the Vampire Slayer, Ally McBeal and he was the voice of Clifford the Big Red Dog cartoon series.

Ritter, whose father was country music singer and actor Tex Ritter, had four children and was married to Amy Yasbeck.

"All of us at ABC, Touchstone Television and The Walt Disney Company are shocked and heartbroken at the terrible news of John’s passing. Our thoughts and prayers are with his wife and children at this very difficult time," said an ABC spokesman.

John Ritter with wife Amy Yasbeck at the 2002 Emmy Awards

Ritter with Jane Curtin (left) and Tyne Daly at the 1984 Emmys