Upon contact, you lose health but gain one to three coins (two to four coins with the PHD) (previously one or two, prior to the patch immediately following the Halloween Update); each one could be a penny or a nickel. The machine will take hearts from your base health and will ignore all your Soul Hearts unless your base health is at one half heart. It is possible to be killed by this machine. In levels before The Womb, the machine will take a half-heart of health with each use. In 'The Womb' levels and later, due to the persistent damage aura in that environment, the machine takes a full heart each time, and will kill you instantly if your base health is at one or one half of a heart, regardless of Soul Hearts.
Alternatively, you can bomb it. This will destroy the Blood Donation Machine and give you a random drop of hearts and/or money.The Blood Bag can also be dropped if you make a large number of donations. The Blood Bag will drop after an average of 8 uses, though the random element can require it to take many more. This risk should be considered when pursuing the Blood Bag, however it will not only grant an extra heart container, but it will heal five hearts (thereby covering the cost of getting it in pre-womb levels). If the player enters an Arcade with enough pennies, it is almost guaranteed that a Blood Bag can be attained, as you can donate and then use the pennies on the other games to restore life to donate more. This method is especially effective when possessing the Lucky Foot, as winning at the shell game becomes a 50% chance. Should the player run too low on hearts, they can bomb it to try and replenish some of their spent health, or if lucky enough, attain the Blood Bag anyway. After dropping a Blood Bag, the Blood Donation Machine will explode.
With the Wrath of the Lamb DLC the Blood Donation Machine is also capable of dropping a Dead Dove, Portable IV bag, or Guardian Angel, this makes going after the Blood Bag riskier as there is a higher chance that the hearts won't be recovered. The machine will also use Eternal Hearts before your base health.
There are a few ways to use the blood donation machine without taking damage. All of these require that you make contact with it:
- Using invincibility granting items such as the Book of Shadows and My Little Unicorn.
- Using the A Pony item's charge.
- Right after the Whore of Babylon item is activated (when you get down to 1/2 a heart) you can quickly use the Blood Donation Machine again (Sometimes even a second time with perfect timing) without it removing your final 1/2 a heart.
- If you hit it right after having received damage from another source (including another Blood Donation Machine, but not the same machine) you won't take additional damage for a very short moment. You can use the machine freely during that time, if you time it well.
- Due to the double damage, and thus double grace time, in The Womb and Sheol, the same Blood Donation Machine can be used twice while only consuming one heart if done with good timing.
- The combination of Yum Heart and Habit allows you to use the blood donation machine for free. (Except for in the Womb, of course)
- Donating to the Blood Donation Machine is the method for unlocking Mom's Bottle of Pills.
- It is worth nothing that if you get the Blood Bag with ???, it will give you only 1 soul heart making the Blood Donation Machine useless without an invincibility item.
- Items that make Blood Donation Machine more viable are Yum Heart, Charm of the Vampire, and Little C.H.A.D. as these can create several hearts worth of health per level which can be spent on the machine. In Wrath of the Lamb, Child's Heart trinket is also very useful for the same reason.
- You can summon a Blood Donation Machine by using the Temperance Tarot Card.
- The Blood Donation Machine works very well with the Whore of Babylon item if you have soul hearts because it allows you to lower your health to half a hearth while keeping your soul hearts.
- Having the Bloody Penny will be a great help, as it has a 50% chance to drop half a heart upon getting a penny.
- Using my little unicorn, the Chariot, Book of Shadows or any other items that let you be invunerable will let you use the blood bank any amount of times.
- Theres a Bug in 1.3, that the player can use it without dying when all hearts are gone. It will be a empty glowing heart. So either you get lots of cents, or you force him to give you the blood bag or the blood donation item. you will die on next hit from an enemy if the Players Health is still empty