Rulings

• 2010-06-15
  If this card is not on the battlefield at the time it resolves, then you can’t sacrifice it. You still perform the search and put any creature cards you find onto the battlefield.
• 2004-10-04
  In a multiplayer game, it triggers if at least one opponent controls three or more creatures.
• 2004-10-04
  You choose how many cards to put onto the battlefield during the resolution after you look through your library. You do not choose as the ability goes on the stack.
• 2004-10-04
  This triggered ability only triggers if your opponent controls 3 or more creatures at the beginning of upkeep. This condition is checked again on resolution.
• 2023-09-01
  Defense of the Heart's ability will check if an opponent controls three or more creatures as your upkeep begins. If none of them do, the ability won't trigger at all. If an opponent does, the ability will check again as it tries to resolve. If none of your opponents control three or more creatures at that point, the ability won't do anything. The opponent that controls three or more creatures as the ability resolves doesn't have to be the same opponent that controlled three or more creatures as it triggered.
• 2023-09-01
  If Defense of the Heart leaves the battlefield while its triggered ability is on the stack, the ability will still resolve as normal.