A cold heart:
* Meaning: Someone who lacks empathy, compassion, and kindness. They are often perceived as unfeeling, indifferent, and perhaps even cruel.
* Example: "He had a cold heart and showed no remorse for his actions."
A warm heart:
* Meaning: Someone who is caring, compassionate, and kind. They are often described as generous, empathetic, and understanding.
* Example: "She had a warm heart and always went out of her way to help others."
Essentially, the idiom highlights the difference between someone who is emotionally distant and someone who is emotionally open and caring.