An Croíbhriseadóir

Roughly the size of a beer coaster, and forged from crude iron, An Croíbhriseadóir is a cold metallic disk with small sharpened spikes on one side and usually the owners emblem on the other.

When placed over the heart of a creature and locked into place, emblem out facing outward, the spikes bury under the skin and wrap themselves around the wearer's heart. Blood begins to pump through the disk, filling in the emblem facing outwards. When unlocked and removed, the emblem can be seen scarred into the wearer's skin. This rare artifact is most commonly seen as a tool implemented by orc pirates and traffickers of Hibernia as a means of keeping prisoners compliant. 

Can only be used on humanoid creatures of a medium size or smaller, and once attached to a heart it can only be removed by magical means.

There is a terrible beauty in the simple craftsmanship behind this item. While you wear this item, you lose 10HP per hour, until your total current hit points are drained down to 1. It has no effect if you are already unconscious or dead.