Heartworm is a potentially fatal disease in dogs. It is transmitted by mosquitoes but is easily prevented by giving a monthly chewable tablet. Dogs need to be treated throughout their whole life to ensure protection from heart disease associated with heartworm infection.
You will need to visit the vet for advice as a blood test may be required prior to starting adult dogs on prevention. There is also a yearly heartworm injection that is available for dogs over 9 months old.