In a series of photos posted on Merelize van der Merwe’s Facebook page, the 32-year-old was shown clutching the bloodied organ.
“Ever wondered how big a giraffe's heart is?” she wrote in a caption. “I'm absolutely over the moon with my BIG valentines present!!!”
In a separate Facebook post Ms Van Der Merwe, who said she had been waiting to hunt a “big black giraffe bull” since 2016, was pictured holding a gun next to the lifeless body of a large giraffe.
“I've hunted more animals then I can count but I still get excited every single time,” she said.
The trip, organised by her husband as a Valentine’s Day present, took place near Sun City, northwest of Johannesburg.
Describing the giraffe, Ms Van Der Merwe said: “I couldn't believe my eyes, BIG BLACK and OLD, so old that he was way over his time and the owner didn't know if he will last another 3 months!!!
“My wonderful husband knew this was my dream and fully supported me from a romantic 5 star weekend away to roughing it again in the heat and bush.
“I was literally like a little child for 2 weeks and counted down the days.”
After killing the 17-year-old giraffe – a species the International Union for Conservation of Nature lists as “vulnerable” – Ms Van Der Merwe said she was “flooded with emotions as I've been waiting years to have this opportunity!!”
She claimed killing the animal would mean “a new bull can take over and provide new strong genetics for the herd”.
Her posts were strongly criticised in dozens of comments left on her Facebook page.
“I am completely SHOCKED by what you did to one of the most humble, endearing and beautiful animals on the planet,” wrote one. “Shame on you,” said another.
Elisa Allen, director of the UK branch of the People for the Ethical Treatment of Animals (PETA) group, described her actions as “bloodlust paired with a burning desire to show off”.
The Independent contacted Ms Van Der Merwe for additional comment.