A 23-year-old male Andean bear named Cisco died Monday during an emergency veterinary exam, according to the Smithsonian’s National Zoo.

Zoo officials said an exam showed Cisco had large amounts of liquid in his lungs and abnormal soft-tissue masses in his chest cavity, resulting in difficulty breathing. While performing a procedure to remove the fluid, Cisco went into cardiopulmonary arrest.

Veterinarians, due to Cisco’s grave prognosis, made the decision not to resuscitate him and let him humanely pass pain free and quietly.

“Cisco was important to the Andean bear population living in zoos,” said Craig Saffoe, curator of Andean bears at the Smithsonian’s National Zoo. “Having come to the National Zoo at 20 years old, he proved that older male Andean bears are quite capable of producing offspring."

"He helped us learn more about Andean bears, and we are sharing everything we have learned about their husbandry, breeding, nutrition and veterinary care from him and our other bears with colleagues in other zoos and in Peru to help the species.”

Male Andean bears in human care, on average, live into their early 20s. A final pathology report will provide more details in the coming weeks.

Born in 1993 at the Calgary Zoo, Cisco came to the National Zoo on loan from the Queens Zoo in New York in September 2013. During his time at the National Zoo, he sired two male cubs born in November 2014. Those cubs, Mayni and Muniri, now live at Nashville Zoo.

Andean bears, also known as spectacled bears, are South America’s only bear species. As their name suggests, they live in the Andes and outlying mountain ranges. Andean bears are listed as vulnerable on the International Union for Conservation of Nature’s Red List of Threatened Species, and it is estimated that there are only 2,000 left in the wild.

The Zoo’s adult female bear, Billie Jean, can be seen at the Andean bear exhibit.