Golem's Heart
Scars of Mirrodin — uncommon
Artifact
Golem's Heart rulings:
2011-01-01: Unlike Golem Foundry and the Smith cycle, Golem’s Heart’s ability triggers whenever any player casts an artifact spell, not just when you do.
2011-01-01: Whenever a player casts an artifact spell, Golem’s Heart’s ability triggers and goes on the stack on top of it. It will resolve before the artifact spell does.