Proheart is a tablet used for the prevention of heartworm disease in dogs. Proheart Tablets contain the active ingredient Moxidectin and are given once a month for the prevention of heartworm disease caused by the parasitic worm Dirofilaria Immitis in dogs. Proheart eliminates the heartworm larvae that infect the dog during the previous month. Heartworm is spread by infected mosquitoes. Heartworm disease is very serious and can cause death. Treatment is very involved, complex and expensive, therefore prevention is preferable to the cure.