Mirage's Heirloom is called Too Much Witt in Apex Legends
Butterfly Knife is Octane's Heirloom
Pathfinder has Boxing Gloves for his Heirloom set
Rampart's Heirloom set is the Problem Solver and resembles a spanner
The developers and designers gave Valkyrie a melee called Suzaku for her Heirloom
One of the most interesting looking Heirlooms in Apex is Wattson's Energy Reader
Lastly, for now, Wraith has a Kunai