"Wolf's heart and dog's lungs" is an idiom that refers to a cruel or ungrateful heart. So why use wolf's heart and dog's lungs as a metaphor for a cruel heart.

In Chinese medicine, there is no mention of wolf's heart and dog's lungs being inedible. The wolf's heart and the dog's lungs are not poisonous; they are perfectly edible, just like any other animal organ.

People in some places don't eat dog's internal organs because of different local customs. For example, cat meat, this side of the people never eat, but in Guangzhou side of the food prevalent, considered a delicacy. Some people don't eat dog's offal, which is related to the fact that dogs will eat poop, and they think that dog's offal is very dirty.