About 500 dogs have died and more than 5,550 became ill after receiving ProHeart 6 shots, given twice a year at veterinarian clinics. The Food and Drug Administration says not all the deaths and illnesses are attributed to the medication.
If your dog has taken the medication, look for symptoms such as vomiting, diarrhea, seizures or lethargic behavior.
The FDA believes that the shots may cause heart and liver problems.
Dog owners were urged to consult veterinarians about other medications to prevent heartworm.