Sheffield died Friday of a heart attack at his home in Chula Vista about four hours after he fell off a ladder while pruning a palm tree, said his wife, Patty.
"He was a jungle boy to the end," she said, noting that her husband of 51 years wasn't too high in the tree when he fell, but "sometimes he was way up there."
The son of British actor Reginald Sheffield was 7 when his father saw an advertisement in the Hollywood Reporter that asked, "Do you have a Tarzan Jr. in your backyard?"
The curly haired Johnny Sheffield beat out more than 300 other youngsters for the role of Boy in the 1939 movie "Tarzan Finds a Son!," in which Tarzan and Jane ( Maureen O'Sullivan) wind up adopting the young child whose parents were killed in a plane crash in the jungle.
Sheffield, who had appeared in "On Borrowed Time" on Broadway in 1938, recalled in a 1997 Times interview that there were two parts in testing for the role of Boy.
"The first was just talking to Weissmuller, and that was no problem," he said. The second part was a swimming test, which for young Sheffield presented something of a problem: He couldn't swim.
The swimming test with Weissmuller, the winner of five Olympic gold medals in swimming, was held at the Hollywood Athletic Club.
"He jumped into the deep end of the swimming pool," Sheffield told The Times in 1997. "He knew I couldn't swim. He said, 'Jump in.' I jumped in the deep end and he took my arm and set me on his knee. He said, 'You're doing fine. Hold your breath, we're going under.'
"We [later] did a lot of those scenes like that in the movies, where I was holding on to him underwater and swimming. We got out of the pool, toweled off and he said, 'This kid can swim fine.' "
From 1939 to 1947, Johnny Sheffield played the leather-loincloth-clad Boy in eight Tarzan films, including "Tarzan's Secret Treasure" and "Tarzan and the Amazons."
Weissmuller was always "kind and tender toward me," Sheffield told the Associated Press in 1984, shortly after the actor he called Big John died at age 79.
"He was like a father to me," Sheffield said. "He was always looking out for me. We worked with a lot of live animals, and a lot of times, when they got tired, the animals would get feisty.
"There was this one big chimp who got pretty mad one day and was about to bite me while we were on the set. But Big John stuck his leg between me and the chimp, and he was the one who was bitten."
Sheffield attended school on the MGM lot while making the Tarzan films and went to public school when he was not.
"You can imagine what it was like at school: Here comes the son of Tarzan!," he said in a 1997 interview with the San Jose Mercury News. "I had to learn how to take care of myself. This is a lot of pressure on a kid when he's trying to figure out who he is and where he's going in life."
After appearing in his final Tarzan film, "Tarzan and the Huntress," in 1947, Sheffield landed the starring role in the 1949 film "Bomba, the Jungle Boy," the first in a dozen low-budget Bomba movies made at Monogram Pictures.
"I loved it because I was now the star," he told the San Jose Mercury News in 1997. "We filmed them all on a sound stage, but I was amazed at the production quality we got in them."
But as Sheffield said in the 1984 AP interview, "I wasn't into the crowds and adulation. You got to love it to be in that business."
After "Lord of the Jungle," the final Bomba movie in the series, was released in 1955, he left the film business.
Sheffield, who was born in Pasadena on April 11, 1931, earned a degree in business from UCLA and moved to Yuma, Ariz., where he worked for a large company that farmed various crops.
He later went into the real estate business in Malibu and Carmel, then spent many years working for a corporation that imported lobsters from Baja and became a contractor whose projects included restoring a couple of buildings in San Diego's Gaslamp Quarter.
Despite being out of the limelight for decades, Sheffield continued to receive fan mail.
"The mail always says, 'Hey, we want to thank you a lot for some good times at the movie show,' " he said in the 1997 Times interview. "They watched the movies, went home and put up a rope and started swinging."
Besides his wife, Sheffield is survived by his sons, Patrick and Stewart; his daughter, Regina; his brother, William, and a grandson.