All heart is a phrase that describes someone who is very kind, generous, and sincere. The antonyms for this phrase are cold, unfeeling, and insincere. Someone who is described as cold has a lack of warmth, emotion, or friendliness. An unfeeling person is indifferent or lacking in empathy, and someone who is insincere is not genuine or honest in their actions or words. These antonyms represent the opposite of what it means to be all heart. When we encounter someone who is all heart, we are often drawn to their warmth and generosity, whereas individuals who exhibit these antonyms may leave us feeling cold or uncomfortable.