WASHINGTON -- Ling-Ling, the giant female panda who delighted visitors to the National Zoo for more than two decades, apparently died peacefully of heart failure.
Preliminary results of a five-hour autopsy conducted Wednesday found evidence that the right chamber of Ling-Ling's heart was enlarged, which apparently led to irregular heart rhythms and then a quick, painless heart failure, Richard Montali, the zoo's veterinary pathologist, said Thursday.
Additional microscope tests on her tissue will be conducted over the next two weeks to rule out other, less likely explanations for the enlarged heart, such as an infection, before a final cause of death is determined, he said.
But the preliminary indications are that Ling-Ling died from heart failure due to the normal aging process, he said.
Ling-Ling, found dead Wednesday in her outdoor enclosure, was 23 years old, the oldest panda in a zoo outside of China. In the wild, pandas rarely live beyond their teens.
'She died without any evidence of a struggle or suffering, for which were all thankful,' Montali said.
'She's lived a long life. The heart muscle eventually starts to lose its elasticity and efficiency,' he said. 'This is a natural cause. There's no evidence of any problems from her past or anything unusual.' He added that there was 'clearly no evidence of accident, foul play, vandalism or anything else.'
'She just died quietly and peacefully. The final event was heart failure -- something we all hope could happen to us. There was no lingering,' he said.
Ling-Ling, who mated with the male giant panda Hsing-Hsing to produce America's short-lived first cub, was a gift from the Chinese government following President Richard Nixon's historic 1972 visit to Beijing that started the process of restoring diplomatic relations between Washington and the communist giant.
Ling-Ling's first cub -- the first born in captivity in the United States -- died of pneumonia in 1983 three hours after it was born. A year later, her second cub was stillborn.
Ling-Ling was born in the wild in 1969 or 1970 and arrived at Washington's National Zoo with her mate on April 16, 1972.
Her name is a nickname for Chinese girls and refers to the bells they sometimes wear on their wrists.
Giant pandas are solitary and pair only for breeding. Ling-Ling and her mate lived in separate quarters in the air conditioned Panda House, where they quickly became the zoo's most popular attractions.
In March 1981, the London Zoo lent its male panda, Chia-Chia, to mate with Ling-Ling but the pair proved incompatible.
Mating attempts with Hsing-Hsing resumed in 1982, and during that year and in 1983 artificial insemination was also attempted with Chia- Chia's sperm, flown from London.
After eight years of failed attempts at natural and artificial insemination, Ling-Ling and Hsing-Hsing mated, and she gave birth July 21, 1983, to a 4.8-ounce male cub that died three hours later of pneumonia.
On Dec. 6, 1983, a potentially fatal kidney ailment was detected in Ling-Ling and treated with antibiotics and blood transfusions.
In December 1984, Ling-Ling mauled a zoo keeper who turned his back on the animal to retrieve a piece of bamboo inside her pen. The keeper recovered.
There are about 1,000 giant pandas surviving in China.
