 During their time at the National Zoo, the pair had five cubs, but none of them survived past a few days.Ling-Ling died suddenly from heart failure on December 30, 1992, at which time she was the longest-lived giant panda in captivity outside China.Hsing-Hsing would go on to pass her record when he was euthanized by zookeepers on November 28, 1999 at the age of 28 due to painful kidney failure.