Upon activation, Isaac gains an Eternal Heart. If you already have an Eternal Heart, you will gain a new heart container upon activation.
Although you cannot gain more than twelve hearts through the use of this card, it is a viable line of defense as additional Eternal Hearts can still be gained.
- Habit - Heart Containers will be added much quicker if Isaac takes damage. In addition to having the Habit, having either or both of The Wafer/Scapular, or The Battery/9V combos leads to technically infinite heart containers. Though the red heart containers are capped at 12, when used in addition with Guppy's Paw, the player can create a ridiculous amount of souls hearts on one floor by swapping the two items. This could also effectively remove the need for the Scapular.
- This item represents a holy card: a small, mass-produced devotional image similar in size to a baseball card, with a simple reproduction of a holy icon printed on one side and often a short prayer printed on the opposite side, they are meant to be carried with a believer or situated in a familiar place and act as a focus for prayer and devotion in everyday life.
- Even though the Prayer Card is marked as a "Special Item" in the game's code, it is not actually a special item.