Heart of Bogardan

Enchantment, 2RR (4)
Cumulative upkeep {2} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

When Heart of Bogardan's cumulative upkeep isn't paid, it deals X damage to target player and each creature he or she controls, where X is twice the number of age counters on Heart of Bogardan minus two.¹
Illus. Terese Nielsen

Gatherer Card Rulings [Nov 2009]

• 4/1/2008: In other words, if you sacrifice Heart of Bogardan rather than pay its cumulative upkeep, X is equal to the amount of mana last spent to pay its cumulative upkeep.

Format Legality	Legal in Vintage, Legacy Banned in Extended, Standard, MTGO Classic
Printings (1/6)	Weatherlight (Rare)