You Die You Lose a Heart

Whenever you die you lose a heart, if you lose all of them you will be forced to go into spectator mode. This is similar to normal hardcore in Minecraft but somewhat forgiving.

Limit the maximum amount of hearts with /gamerule maxHearts (by default set to 20 hearts) and whether players can even get hearts with /gamerule canRestoreHearts true/false (by default set to true)

You can replenish hearts by eating enchanted golden apples. This gives enchanted golden apples actual use outside of pvp.