Golem's Heart

• WWizards of the Coast2011-01-01
  Official Ruling
  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.
• WWizards of the Coast2011-01-01
  Official Ruling
  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.

Rulings via Scryfall