CHICAGO - Scientists for the first time have grown human heart valves using stem cells from the fluid that cushions babies in the womb - offering a revolutionary approach that may be used to repair defective hearts in the future.

The idea is to create these new valves in the lab while the pregnancy progresses and have them ready to implant in a baby with heart defects after it is born.

Dr. Simon Hoerstrup, a University of Zurich scientist, speaks at an American Heart Association conference Tuesday, Nov. 14, 2006, in Chicago. Scientists for the first time have grown human heart valves using stem cells from the fluid that cushions babies in the womb - offering a revolutionary approach that may be used to repair defective hearts in the future. [AP]

The Swiss experiment follows recent successes at growing bladders and blood vessels and suggests that people may one day be able to grow their own replacement heart parts - in some cases, even before they're even born.

It's one of several sci-fi tissue engineering advances that could lead to homegrown heart valves for infants and adults that are more durable and effective than artificial or cadaver valves.

"This may open a whole new therapy concept to the treatment of congenital heart defects," said Dr. Simon Hoerstrup, a University of Zurich scientist who led the work, which was presented Wednesday at an American Heart Association conference.

Also at the meeting, Japanese researchers said they had grown new heart valves in rabbits using cells from the animals' own tissue. It's the first time replacement heart valves have been created in this manner, said lead author Dr. Kyoko Hayashida.

"It's very promising," University of Chicago cardiologist Dr. Ziyad Hijazi said of the two studies. "I don't doubt" that it will be applied one day in humans, he said.

One percent of all newborns, or more than 1 million babies born worldwide each year, have heart problems. These kill more babies in the United States in the first year of life than any other birth defects, according to the National Institutes of Health.

Heart valve defects can be detected during pregnancy with ultrasound tests at about 20 weeks of pregnancy. At least one-third of afflicted infants have problems that could be treated with replacement valves, Hoerstrup said.

"It could be quite important if it turns out to work," said Dr. Robert Bonow, a Northwestern University heart valve specialist.

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