The zoo announced the death on Wednesday evening, saying the calf – whose name, Amara, was due to be revealed shortly – died suddenly on Friday afternoon.
“The ‘little leggy watermelon,’ as it was affectionately known, was born in late November and in a relatively short time has captured the hearts of guests and caretakers,” the zoo said on social media.
“She was found unconscious on Christmas Eve evening and it was unfortunately confirmed that she was deceased.
“Preliminary results from Taronga’s veterinary team indicate a potential problem with her heart.”
Vets are still investigating and keeping a close watch on the calf’s parents, Kambri and Fergus.
The zoo said there was “no indication of trauma or mishap.”
“She was a much-loved member of the Taronga family and her passing is understandably heartbreaking for all who knew and cared for her,” he said.
“Our mother and calf duo are doing really well,” said Renae Moss, ungulate keeper at Taronga Zoo at the time.
“Kambri is an excellent mother. She is extremely maternal and very protective and our calf is getting more and more confident every day, more and more energetic.
Baby animals celebrate their very first Christmas
“In the beginning she slept most of the day – slept and fed like any newborn baby, but now she’s exploring her surroundings and today she takes a really good look at her exhibit.”
Ms Moss said there are less than 3,000 pygmy hippos left in the wild, making births in zoos “extremely valuable”.