A black heart represents sadness and loss. Black is a very mysterious color. Some of the connections generated by black will be sadness, death and sin, but the positive black can show elegance, enthusiasm, confidence, mystery, power and power.
You can think of some black positive and negative impressions in the language. For example, some beautiful things can be described as black tie, or an expert (not just in martial arts) can be described as black belt. On the negative side, a person may be a black guard, black hearted, black sheep, or black listed.