Chocolate should never be ingested by cats because it is toxic to them and can cause serious issues such as vomiting, diarrhea, low blood pressure and seizures. According to PetMD, too much chocolate can also cause death in cats.
Chocolate is toxic to cats because it contains theobromine and caffeine, which are part of a group of chemicals called methylxanthines. Generally, darker chocolate contains higher levels of methylxanthines, so it is more hazardous to cats than milk chocolate. When cats ingest any form of chocolate, it is best to get them to a veterinarian immediately. Veterinarians can diagnose chocolate poisoning and determine the best method of treatment.