We dog owners, know we should use a preventative heartworm medicine. The American Heartworm Society and our vets keep telling us to use one, but what is it?

Preventative heartworm medicine is available for both dogs and cats. As dogs are more likely to contract the disease, far more dogs are regularly given heartworm preventatives than cats. But whether you're looking out for the health of a canine or feline friend, the principles behind heartworm medicines are the same.

The key thing is that heartworm preventatives do not actually stop your pet becoming infected with larval heartworms. Instead, they assume that to prevent a mosquito bite is pretty much impossible, so better to deal with the situation after such a bite. The active ingredients contained in all forms of preventative heartworm medicine are able to safely destroy larval heartworms that have been in the animal's system for up to a month.

So, every time you give your dog its heartworm medicine, you are actually destroying all heartworm larvae that have been passed to your pet by an infected mosquito, during the previous thirty days. This is an important point, because if you only use heartworm medicine on a seasonal basis, you must ensure the last treatment is given after mosquito activity has stopped. It also, means that if you forget a treatment, your pet could be harbouring older, more developed heartworm larvae, which are more difficult to destroy than those under a month old.

Only four drugs are used as heartworm preventatives. Ivermectin and Milbemycin oxime are used in heartworm pills. Selamectin and Moxidectin are found in topical heartworm medicines and Moxidectin is used in the heartworm injection and Proheart heartworm pills. All, have been found to be 100% effective at preventing heartworm disease, but only if used absolutely correctly, so it is imperitive that you read the instructions whatever dog heartworm medicine you choose.

A few products, such as Revolution and Advantage Multi can be used to prevent heartworm disease and control other parasites (both internal and external). The combination of flea control and heartworm prevention is a reasonably new innovation. This change has meant more pet owners than ever before are automatically using a heartworm medicine as it is no more work (and not too much more cost) than just using an effective flea treatment which they would do anyway.

Preventative heartworm medicine for dogs and cats is extremely effective. It isn't just a matter of protecting your pet either. Every dog regularly given heartworm pills is one less host for breeding heartworms. That means future generations of the parasite are fewer, and so too are the number of dogs infected with the disease in future.