When the player (or one of the player's familiars) takes damage, there is a 15% chance that one Heart will be regenerated and added to their health. This effect can activate multiple times in a single life.
It is very hard to come across, but incredibly powerful - so powerful, in fact, it's the only way to progress on one of the game's floors.
I was able to grab it in the Black Powder Mine. It's alright. There are two other +10% damage items you could get instead of this one, but it's cool because vampiric items heal you for 20% of the damage dealt by guns.
Its effect is applied on entering a new floor. It also affects your shop: if it has items for sale, chests will pay more for them.
It is a rare drop from Blue Devils (the midboss of the Supply Depot). When worn, it grants the player 1 health per second. Any health chests spawned by Generators are also health fountains, because the Ring of Chest Vampirism allows the player to hit blue flames without taking damage.
This item can have a lot of positive effects when given to the right character.
A ring imbued with dark magic, it is whispered that this relic will sometimes allow the bearer to draw the life force of an enemy into their own body, even in death.