It started with a murmur and ended with cheers: in 1994, Karen the orangutan made veterinary and medical history by becoming the first great ape to undergo open-heart surgery.

When two-year-old Karen went in for her check up, Zoo veterinarians heard a heart murmur. Tests showed a hole in the wall between the two upper chambers of her heart. It needed to be fixed, but open-heart surgery had never been done on a zoo animal before, as far as anyone could determine. The procedure is fairly common for human babies, and since ape and human hearts are almost identical, the “fix” seemed doable. To accomplish the operation, more than 100 people came together to help the young ape, including two world-famous cardiac surgeons, Dr. Stuart Jamieson and Dr. Jolene Kriett from UCSD Medical Center, who performed the seven-hour procedure. When Karen developed post-operative respiratory problems, anesthesia expert Dr. Mark Greenberg of UCSD set up an intensive care unit at the Zoo hospital with a volunteer staff for 24-hour nursing care to help Karen recover.

The surgery made headlines, and Karen’s story touched people—she received get-well cards from all over the world. Karen returned to the orangutan habitat, where she continued to grow and thrive. Today, she is still going strong as part of the Zoo’s orangutan troop.