Oct. 17, 2002 -- Champion free diver Audrey Mestre took a single breath, then dove 561 feet to try to try to break a world record. But the 28-year-old French woman did not make it back up alive.

She blacked out and died Saturday after her plunge into deep waters near La Romana, 81 miles east of Santo Domingo, Dominican Republic.

Mestre was attached to a 200-pound weight mounted on a steel cable to help her get to the proper depth. She was trying to break the "no limits" dive world record of 531.5 feet set by her husband, Francisco "Pipin" Ferreras in January 2000. Together, they were the most famous free-diving couple in the world.

But on Mestre's way up to the surface during that fateful dive, she blacked out at a depth of 300 feet. A safety diver activated an emergency inflatable device, and rushed her to the surface using his inflatable jacket. Ferreras desperately tried to revive her using mouth-to-mouth, but it was too late.

The woman who had become the world's best free diver had died. The dive was only supposed to take three minutes, and she had been underwater more than nine minutes without oxygen.

Dangerous Sport Requires Training

Free diving is dangerous, and in some cases deadly sport. There are about 5,000 free divers around the world, and an estimated 100 die each year. The divers say there is a sense of euphoria being so far down, and liken the experience to being in outer space. It puts the body through great physiological changes, which in some cases leads to death.

Unlike scuba divers, free divers do not use oxygen tanks, and instead, simply take a deep breath and dive at least 400 feet, the equivalent of a 40-story skyscraper. Free divers basically push their bodies to the limit: as they descend hundreds of feet, their heart rates slow to as low as 14 beats a minute, their lungs shrink and blood surges from the extremities to the heart and the brain.

To counteract the impact, divers must train in proper breathing techniques. The lower third of the lungs contain two-thirds of the blood supply, and it is the blood that holds the oxygen and carries it throughout the body.

So divers must use the muscles of their diaphragm when they breathe, to get the oxygen into that lower part of the lungs.

The proper breathing allows free divers to lower their heart rate, reduce the carbon dioxide levels in their body, and make room to fill every possible space with air.

Blackout Biggest Risk

To get back to the surface, divers inflate a balloon that quickly carries them to the surface. Those last few feet, as your body readjusts to the nearing-the-surface pressure, are especially risky.

"The biggest risk is shallow water blackout," free diving teacher Kirk Krack diver told Good Morning America in an interview that aired in Oct. 2000. "That's upon your return to the surface. You've used up so much oxygen that your body senses the low level and it decides to conserve oxygen for you. And it basically shuts you off, turns the switch off and you go unconscious."

Blackouts like Mestre's account for 99.9 percent of deaths, Krack said.

Ferreras told WABC's Bill Ritter that he is broken up about his wife's death, but believes she died doing something she loved. Mestre was a French university student studying marine physiology when she met Ferreras.

"I chose him as the subject of my testing because he was the world champion free diver," Mestre told Ritter in an interview that aired in March on 20/20 Downtown. She fell in love with him in "about two days," she said.

As a posthumous honor, the International Association of Free Divers, a Miami-based organization that monitored Mestre's dive, will recognize her 558-foot unofficial practice attempt on Wednesday as the new world record.

A champion diver himself, Ferreras said he will not be deterred from diving again — at least one more time. He is planning to do a dive in Mestre's memory next year.

"I'm not going to break her record," he told Ritter. "I'm going to reach the same depth she reached in training… After that dive, I'm going to retire."