Hi Todd,

Thanks for your question.

Heartgard absolutely needs to be given monthly to prevent a serious canine heartworm infection that can be life-threatening. Heartworm is spread by mosquito bites and it’s found in all 50 US states and it’s also present in Canada. Mosquitoes spread and the risk period is really going to vary depending on which times of the year the mosquito population remains active and that’s going to vary massively between different areas. So in some parts of the country or in some parts of the world, that might be a year-round risk but in other areas, it’s going to be a much more narrow window where the potential for your dog to contract and to suffer from heartworm is a risk.

While the general recommendation may be given for a specific area, it may be that certain years have a longer treatment period. For example, if an autumn is particularly mild and then it might be that mosquitoes are active for longer in that year. If the spring comes early, then it might be that where 6 months would normally be able to cover and prevent heartworm infection, you might need to spread it out to 9 months. Because of this variation and the serious nature of heartworm infection, some people may prefer to play it safe and treat or if their vet recommends treatment with heartworm preventatives for longer than may be absolutely necessary, just airing on the side of caution.

Please discuss these concerns over with your vet as they’re going to understand what the local risks are, risk periods, what the mosquito activity is like and be the best person to give a recommendation about what’s appropriate for your dog.

Good luck.

Dr. Alex Avery