It would have 'melted your heart' [=it would have filled you with compassion, sympathy, etc.] to see her lying in that hospital bed.
Her anger 'melted away' when she saw that he was truly sorry.
He seemed to 'melt into' thin air. [=he seemed to disappear]
(..) us something and Emmet is... - I told you I was a nobody. - Oh. I can't break him. Take him to the melting chamber. You're gonna melt me'? Am I gonna die? President Business. I have him right here, sir. Yes, we've told him he'll live so he doesn't try to escape, but, um... (..)2014 The Lego Movie