Defense of the Heart asks opponents to maintain a small board or risk letting you find two creatures directly from the library. At the beginning of your upkeep, it triggers if an opponent controls at least three creatures. If that condition still holds when the ability resolves, the enchantment is sacrificed and the two searched creatures enter under your control.
Forbidden Orchard can help create the required opposing creature count while fixing mana. The creature pair can serve different purposes: Avenger of Zendikar plus a supporting threat can build a board, while a deck with red might choose Kiki-Jiki, Mirror Breaker and Zealous Conscripts for a specific combo. Entry abilities work, but cast triggers do not, because the creatures are put onto the battlefield rather than cast.
The delay is the card's main constraint. Casting it does not immediately search, and opponents have time to remove the enchantment or reduce their creature counts. A player with three tokens and a sacrifice outlet can deliberately drop below the threshold before the ability resolves. That makes it strongest against boards that cannot easily change their creature count, or when several opponents independently meet the condition. Have a search pair in mind, but keep alternatives available: the best creatures after a turn cycle may be defensive tools or value engines rather than the finish you expected when the enchantment first entered.
