The cake decorator had Bakels bake the cake and provide fondant before she spent two days carving and decorating it.
Photos that Blackburn posted on Make Pretty Cakes social media show a realistic torso and heart made out of chocolate and red velvet cake with strawberry and chocolate Bakels truffle filling, covered with Pettinice fondant.
There are also medical tubes, that are meant to represent blood — but it's really strawberry and blueberry jelly.
Blackburn said the birthday student "loved" the cake as he got to perform surgery before sharing the delicious treat with his friends.
"I made the heart separately so that he could take the heart out and in behind the heart I put 'Happy 21st Birthday'," she explained.
"He said it was great."
Blackburn also pointed out the bizarre research that goes into cake decorating, especially for a heart surgery cake.
"The research that goes into cake decorating is hilarious at times, and if anybody wants to look at my Google history they're going to find the strangest things.
"You know how they always say don't ever Dr Google any health problems you may have because you might see the very worse outcome, well I had to Dr Google 'open-heart surgery'.
"The research for it was a lot if you're a decorator and you really want to know what goes where. At one point, because of all the Google photos, I couldn't tell if I actually put the heart backwards."
After sharing photos of the heart surgery cake on Facebook, she noticed the social media platform blocked one of the images as it was labelled graphic content.
Such a fun cake to make! Interactive cake of human torso during heart surgery for a medical student's 21st birthday. ...
Posted by Make Pretty Cakes on Saturday, 20 July 2019
"Facebook actually blocked the photo for being too realistic. That made me laugh, for a cake decorator, that's a complete win," she said.
That wasn't the only win she got from sharing the incredible photos on Facebook, as she was just commissioned another heart surgery cake from Waikato Hospital to celebrate the heart surgery unit's 30th birthday.
"I'm going to redo it for real surgeons and doctors and I've got to get it right," she said.
Blackburn, who moved from the US with her husband 13 years ago, has made several other challenging cakes that have fooled some.
One included a turntable cake that rotates.
She made the life-sized Linn Sondek LP12 cake for the founder of Linn Products, Ivor Tiefenbru, who was influential in the manufacture and retail of British audio in the 1970s and 1980s.
"I had the record spinning and no one caught on that it was a cake until we went up to it later and cut and everyone was so shocked. For me, it wasn't the biggest, but it terms of fooling people that was a lot of fun."
Another way she fooled someone was when she was asked to make a cake by a man who wanted to prank his wife.
The cake looked innocent in the box, but when opened it has feet at the bottom.
Apparently, she hates feet!
Blackburn said she loves making cakes that are "something out of the norm", including corporate cakes, big cakes and realistic ones.
She also enjoys teaching people and provides classes to anyone who shares her passion.
Blackburn is running the Pettinice Cake show, at the Pakuranga Rugby Club in Auckland on October 19-20.
The show, which is sponsored by Bakels, features a cake competition, demonstrations, classes and where people can purchase the latest tools for their decorating needs.
The theme is art in cake and Blackburn said that all the cakes are delicious.
