The Corrupt Heart is the final boss, fought in Act IV of the Spire. It is very powerful; its innate powers and buffs it gains throughout the fight can prove very difficult to counter. Because of its Invincible buff, it can only take 300(200) damage per turn, rendering strategies that rely on heavy damage less effective. Additionally, it will gain incredible amounts of Strength on its fourth buff and onward, so killing it quickly is also important.
Beat of Death X: Whenever you play a card, take X damage.
Invincible X: Caps all damage and HP loss taken to X each turn.
Painful Stabs: Shuffle 1 Wound into your Discard Pile each time you receive unblocked attack damage.
Medical Kit can be useful against The Heart, as it will allow you to remove the many statuses it will inflict on you, but beware of its Beat of Death power, as it will trigger whenever you play any card, including curses and statuses.