DALLAS - 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 miles per hour.

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.

"What made him so unusual is he developed, literally, hundreds of cars," said Craig Jackson, chairman and CEO of Barrett-Jackson Auction Company. "This guy was 89 years old and he was still developing cars."

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, 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.

"His legacy is the diversity of his life," he added. "He's incredibly innovative. His life has always been the reinvention of Carroll Shelby."

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's a special car. It would do just over three seconds to 60 (mph), 40 years ago," Shelby told the crowd before the sale, held in Scottsdale, Ariz.

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 miles per hour. It is arriving in dealerships now. 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."

Edsel B. Ford, a member of Ford's board of directors, said Friday in a statement that the company had lost a legend.

"Carroll Shelby is one of the most recognized names in performance car history, and he's been successful at everything he's done," Ford said. "Whether helping Ford dominate the 1960s racing scene or building some of the most famous Mustangs, his enthusiasm and passion for great automobiles over six decades has truly inspired everyone who worked with him."

He created the Carroll Shelby Foundation in 1991 to provide assistance for children and young people needing acute coronary and kidney care. According to its website, the foundation has helped numerous children get surgery, as well as provided money for research.

Shelby was born Jan. 11, 1923, in Leesburg, Texas.

During World War II, he was an Army Air Corps flight instructor who corresponded with his fiancee by dropping love letters stuck into his flying boots onto her farm.

After leaving the military in 1945, he started a dump truck business, then decided to raise chickens. The poultry business initially flourished, with Shelby earning a $5,000 profit on the first batch of broilers he delivered. He went broke, however, when his second flock died of disease.

A friend then invited him to become an amateur racer and his success led to his joining the Aston-Martin team and competing in races all over the world.

Shelby had homes in Los Angeles and his native east Texas. Doctors did not immediately release a cause of death.

He is survived by his wife, Cleo Shelby; his three children, Patrick, Michael and Sharon; his sister, Anne Shelby Ellison; six grandchildren and four great-grandchildren. Funeral services were not immediately announced.