If the Devil Room has been visited before picking up Eucharist, an Angel Room will not replace it on the current floor, despite the Angel Room chance displaying 100%. However, Eucharist will still cause the door to remain open.
Synergies
Duality: Both Angel and Devil Room doors spawn after every boss, and the selected door will never disappear.
Filigree Feather: Due to Angel Rooms being guaranteed, a large influx of items can be obtained over time.
Red Key: Devil rooms can still be spawned via the creation of red rooms.
A eucharist is a Christian rite in which bread and wine are transubstantiated into the body and blood of Jesus Christ on an altar and consumed thereafter.
Gallery
Afterbirth+ item concepts, including for Eucharist.
Angel Room Door will spawn whenever possible and remain open and preventing 
Devil Rooms from spawning.
Duality: Both Angel and Devil Room doors spawn after every boss, and the selected door will never disappear.
Filigree Feather: Due to Angel Rooms being guaranteed, a large influx of items can be obtained over time.
Red Key: Devil rooms can still be spawned via the creation of red rooms.
Goat Head: Overridden by Eucharist.
Tainted Lazarus: Eucharist is shared by both characters.
Magdalene Unlocks 
Delirium Unlocks 
The Binding of Isaac: Rebirth
