Did you know that heartworm is carried by the common mosquito and can be deadly to dogs of all breeds and ages? Heartworm can be prevented with a yearly injection from your local veterinarian or with a cost effective monthly preventative such as Heartgard Plus or Valuheart. Dogs can be protected against heartworm from 6 weeks of age; however it is important to have your dog tested for heartworm before starting on a preventative treatment.