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]
(..) - Rupees. - Which is? Uh, buck and a half. What do you want? I wouldn't say no to a tuna melt. Thanos is coming. He's coming. Who? Slow down, slow down. I'll spell it out for you. (..)2018 Avengers: Infinity War