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]
(..) down the mountains, gouging out deep valleys. They're the most powerful erosive force on our planet. A moulin - a shaft in the ice opened by melt water as it plunges into the depths of the glacier. Like the water running through it, the ice itself is constantly moving, flowing down the valley (..)2006 TvShow: Planet Earth Title: Mountains Season: 1 Episode 2