I could not find much on this, but we see Daenerys Targaryen eat a horses heart.
What I want to know what was it really, what was the prop made out out of?
It was made of a gummy bear-like material:
Around 1:50
According to actress Emilia Clarke (Daenerys), the prop she used for the stallion's heart was made of gummy bear-like material, which actually tasted awful, so the difficulty with which she seems to be choking it down is actually a genuine physical reaction. It had to be something she could really bite, chew, and swallow, because it would have seemed fake if she was only miming the act of eating a prop without actually consuming pieces of it.