It gives an extra permanent heart, similar to the golden apple's effects. It can be used up to 11 times, allowing one to have a total of 21 hearts (42 health).
This buffer of hearts can be seen on top of your health bar.
Some notes on how the item works:
1) The item does not need to be activated or selected, it needs only to be in your hotbar to work.
2) When in your hotbar, it will generate "shield" hearts. These hearts seem to work like the absorption buff, stacking with the Tinker's Construct hearts (the TC hearts cover each other with different colors - these hearts are just over that).
3) If you take the item off your hotbar, you keep your current "shield" hearts, but you will not regenerate them; you will start regenerating them once you put the Life Ward in your hotbar again.
4) The "shield" hearts regenerate independently from regular hearts, this can help mid-combat.
How to obtain Edit
The Life Ward is an item dropped occasionally from killing the Life Guardian.
Behavior with other mods Edit
The hearts do stack with the Tinker's Construct hearts.
When using Blood Magic, draining life essence from yourself damages you and ignores the hearts provided by this item.