Golem Heart is in there to help gain life so Chalice of Life can transform quicker. I don't know too much about artifacts so I don't know what other artifact cards would be useful. I'd like to replace it, but I can't think of artifact cards that would help gain life aside from what I've put in already.
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If your referring to Mox Opal I did add it in. And I forgot about Darksteel Citadel, not a bad idea to add it in though.