SAN DIEGO -- An elderly giant panda at the San Diego Zoo has been diagnosed with an incurable heart problem.

The zoo said Gao Gao had a medical checkup Tuesday and was found to have pulmonic stenosis, a narrowing of the pulmonary heart valve.

"Gao Gao has a heart disease that will continue to progress,'' Ryan Sadler, a zoo veterinarian, told CBS affiliate KFMB. "Unfortunately, we can't cure this disease, but we definitely can provide him with excellent medical care and make his quality of life good."

Sadler said Gao Gao was put on medication and is responding well to the treatment. The goal is to keep him "as healthy and content as possible,'' the vet said.

Get Breaking News Delivered to Your Inbox

The condition is most commonly the result of a birth defect. The zoo says symptoms can include a heart murmur, a low tolerance for exercise and fatigue. Gao was diagnosed with a heart murmur three years ago.

The panda, who's about 26 years old, also has high blood pressure. He had a cancerous testicle removed two years ago, according to KFMB.

Gao Gao and two other pandas are on loan to the zoo from China. He lives with the female panda Bai Yun and their three-year-old son Xiao Liwu. Around 1,600 giant pandas are believed to exist in the wild, but those numbers may be growing due to dedicated conservation efforts.