DALLAS (AP) ― Decades after a heart condition forced him to retire from racing, Carroll Shelby still loved to drive muscle cars. Well into his 80s, the legendary car designer spent hours testing his last Mustang Shelby GT500, which sets a new record for horsepower and hits a top speed of more than 200 mph.

A one-time chicken farmer, Shelby had more than a half-dozen successful careers during his long life: champion race car driver, racing team owner, automotive consultant and safari tour operator. His fabled Shelby Cobra sports car became an automotive and cultural icon, and he was later credited with injecting testosterone into Ford’s Mustang and Chrysler’s Viper.

When Shelby died Thursday night in a Dallas hospital, he also was one of the nation’s longest-living heart transplant recipients, having received a heart on June 7, 1990, from a 34-year-old man who died of an aneurysm. Shelby also received a kidney transplant in 1996 from his son, Michael.

Shelby first made his name behind the wheel of a car, winning France’s grueling 24 Hours of Le Mans sports car race with teammate Ray Salvadori in 1959. He had turned to the race-car circuit in the 1950s after his chicken ranch failed. He won dozens of races in various classes throughout the 1950s and was twice named Sports Illustrated’s Driver of the Year.

He already was suffering serious heart problems when he won Le Mans and ran the race “with nitroglycerin pills under his tongue,” his longtime friend, Dick Messer, the former executive director of Los Angeles’ Petersen Automotive Museum, once noted. Soon after his win at Le Mans, he gave up racing and turned his attention to designing high-powered “muscle cars’’ that eventually became the Shelby Cobra and the Mustang Shelby GT500.

“He’s an icon in the medical world and an icon in the automotive world,” Messer said.

The Cobra, which used Ford engines and a British sport car chassis, was the fastest production model ever made when it was displayed at the New York Auto Show in 1962.

A year later, Cobras were winning races over Corvettes, and in 1964 the Rip Chords had a Top 5 hit on the Billboard pop chart with “Hey, Little Cobra.” (“Spring, little Cobra, getting ready to strike, spring, little Cobra, with all of your might. Hey, little Cobra, don’t you know you’re gonna shut ‘em down?”)

In 2007, an 800-horsepower model of the Cobra made in 1966, once Shelby’s personal car, sold for $5.5 million at auction, a record for an American car.

It was Lee Iacocca, then head of Ford Motor Co., who assigned Shelby the task of designing a model of Ford’s Mustang that could compete against the Corvette for young male buyers. Iacocca often joked that Shelby was so persistent he gave him the money and Ford V-8 engines to build the Cobra just to get him out of his office.

Turning a vehicle he had once dismissed as “a secretary car” into a rumbling, high-performance model was “the hardest thing I’ve done in my life,’’ Shelby recalled in a 2000 interview with The Associated Press.

That car and the Shelby Cobra made his name a household word in the 1960s.

When the energy crisis of the 1970s limited the market for gas-guzzling high-performance cars, Shelby weathered the downturn by heading to Africa, where he operated a safari company for a dozen years.

By the time he returned to the United States, Iacocca was running Chrysler Motors and he hired Shelby to design the supercharged Viper sports car.

“He was a great friend and we did some really good work together,’’ Iacocca said Friday in a statement.

Inducted into the Automotive Hall of Fame in 1992, Shelby worked in recent years as a technical adviser on the Ford GT project and designed the Shelby Series 1 two-seat muscle car, a 21st century clone of his 1965 Cobra. His 2013 Shelby GT500 has the most powerful production V-8 engine in the world ― at 662 horses ― and a top speed of more than 200 mph. The model that Shelby test drove sold for $350,000 at a charity auction in January.

“I’ve always been asked, ‘What is my favorite car?’ and I’ve always said ‘The next one,”’ Shelby said, according to Ford’s website. “I’m going to take that back tonight. This is my new favorite car.’’