St Bernard Petcare's Monthly Soluble Heartworm Tablets for Small Dogs (Up to 11Kg's) is an affordable and effective monthly heartworm preventative for dogs that contains 68µg of ivermectin, the most widely used drug to prevent heartworm in Australian dogs for over ten years. Saint Bernard Petcare Heartworm tablets has a wide margin of safety for most dogs, but in particular breeds especially the with the Collie dogs and Border Collies adverse reactions may occur. Always consult your veterinarian for advice.