The Yellow Heart Canister is an item added by Tinkers' Construct , which increases the number of hearts that the player has. To have an effect the canisters must be equipped in the Armor Tab , in the slot on the right with the symbol that looks like the heart canister. Up to 10 can be stacked in this slot to allow for a total of 10 extra hearts (or 20 extra health points). These will not appear above the regular health bar like from the Absorption effect, instead once the health bar is full the red hearts will gradually be replaced by orange hearts. If 10 Red Heart Canisters are already equipped, the additional health from Yellow Heart Canisters will then replace those orange hearts with yellow ones.