Karen Pendleton, who charmed young baby boomers in the 1950s as one of the original Mouseketeers on Walt Disney’s television series “The Mickey Mouse Club,” died on Sunday in Fresno, Calif. She was 73.

Her daughter, Staci Bletscher , said the cause was a heart attack.

Ms. Pendleton was 9 when “The Mickey Mouse Club” made its debut in October 1955, shortly after Disneyland opened in Anaheim, Calif. A tiny girl with long, curly blond hair , she could dance adeptly thanks to lessons she had been taking since she was 3.

“I got the giggles” at the audition, she told The Los Angeles Times in 1995. “I think that may be something to do with why they chose me. They were really trying to find kids who were really down to earth — not real, real professional.”

She joined Annette Funicello, Sharon Baird, Cubby O’Brien, Darlene Gillespie and the other Mouseketeers — all of whom went by just one name, and all of whom wore mouse ears — in a show that featured singing and dancing, educational segments (one starred Jiminy Cricket) and episodic serials. Ms. Funicello, the Mouseketeer who went on to have the most prominent entertainment career, died in 2013.