Gains attack speed up to 100 lives lost after getting this upgrade, Lives above maximum do not count.
Heart of Vengeance is the second upgrade of Path 3 for the Druid. It gives the Druid 1% more attack speed for every one life lost after the upgrade is bought, up to 100 lives. Conversely, gaining lives will reduce Heart of Vengeance attack speed bonuses by 1% per life gained, down to 0% bonus. As of Version 9.0, the default attack speed bonus is 10%; the player needs to lose 90 net lives to reach its maximum speed.
Just as losing lives will increase attack speed, gaining lives will make Druids with this upgrade attack slower. It is best not to use life gaining strategies with this path of upgrades, such as with Benjamin, Support Chinook's Supply Crate ability, or the Spirit of the Forest upgrade.