If you need to kill one to get its heart easily, simply take a flyer with enough stamina and make the Giga chase you to a big body of water where the Giga can’t climb out(off a cliff) and then hit it a couple times until it’s head goes down, it should drown in a couple of mins, easy Giga heart.
I dare you to raise one!! They are savage if you got two high lvl parents (about lvl 140ish) and you get imprinting on it. The thing will become an adult with about 230% melee and basically one chomp any bronto!!! But on the down side you loose your job and your girlfriend
Make 4 metal dino gates and 1 large bear trap. Place three frames and door into an incomplete square and the large bear trap in the I between them. Lure the Giga into the trap and while its trapped place 4th down to make the square. Then just light it up with tranqs