This is out of all the cards ever created.
Current as of 2015 it is WailordEX from Primal Clash with 250 HP.
Actually the highest health card is shadow Lugia, which is banned from tournaments and official events.
As of 2019, the card with the highest health is tied between Shadow Lugia and a Tag Team GX card called Wailord and Magikarp. They both have 300 HP.
Mega Venasaur EX