With regard to the heartbeat magic - you can't do anything that requires GMing. So, if my character looks emotionless but has a quickly-beating heart and I write that it's because she's really happy, you wouldn't know that. It could be out of fright or anger for all you know.
Same with changing the heart beats of others - if you increased my heartbeat it might make me anxious just as easily as happy, even if those have the same BPM.
And for the electric-heart-creature, again it can't have GMing. Agreed upon forms are totally fine, but without that it would just be his own approximation.