A baby panda died Sunday at the Smithsonian's National Zoo saddening the staff of the facility who in the last seven years, had only seen one panda cub survive..

The giant panda cub appeared to be a female and weighed only about four ounces. There were no signs of trauma (meaning she was not crushed by her mother panda Mei Xiang) and her heart and lungs looked good. However, veterinarians found a slightly abnormal liver.

"They don't know yet whether either of those things is significant, and they're still investigating," the Zoo informed. "We'll continue histological evaluation. As we know more, we'll share it with you."

A statement released Sunday morning said that staff at the zoo and volunteers heard a "distress vocalization" from the mother, Panda Mei xiang.

The staff performed CPR shortly after but were not successful in reviving the cub.

People on Twitter and Facebook were saddened by the news.

"The whole story around the death of the baby giant panda is just absolutely heart wrenching," one user on Twitter said.

"Make me want to cry, I am so sorry for the loss. :-(" Said another user on Facebook.

"I hope it is some consolation to the wonderful zoo staff that they are not alone in their grief. We all mourn the loss of 'our' baby," a third user wrote on Facebook.

The death of the baby panda is specially delicate because when the cub was born last Sunday, giving hope to the Smithsonian's giant panda research project.

The zoo hadn't seen a baby born to Mei since seven years ago and the zoo's director Dennis Kelly dubbed it as "one of the best things" that could happen to Washington at the time.