This is out of all the cards ever created.
Current as of 2015 it is WailordEX from Primal Clash with 250 HP.
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.
Actually the highest health card is shadow Lugia, which is banned from tournaments and official events.
Mega Venasaur EX
As of 2020, the Pokemon with the highest hp is Snorlax Vmax with 340 hp, and Buff Padding raises it to a whopping 390 hp.