Heartworm disease is often discussed as an ongoing risk for dogs and cats.  The reality is that the risk depends greatly on the geographic location and lifestyle of pets and people.  Let’s start with a few facts:

  1. Heartworm disease is caused by a worm that lives in the blood vessels around the heart.
  2. Heartworm disease must be spread by a mosquito and cannot be transmitted directly from pet to pet.
  3. The risk of heartworm disease is directly dependent on mosquito exposure and environmental temperature.
  4. Heartworm preventatives are not benign medications, and true risk to your pet should be considered before administering them.


Because we live in a dry climate and mosquitos are uncommon unless you spend time around standing water, the risk of Heartworm disease is low in Colorado.

In addition, the larvae cannot mature in the mosquito unless the environmental temperature is 57degress or above for 2-3 weeks.  Once the temperature drops below 57 degrees, the development of the larvae stops.  This makes heartworm even less common in Colorado due to our low nighttime temperatures.  Mosquitoes are more prevalent in the mountains, but the temperatures are too low to support heartworm disease.

We recommend using heartworm preventatives based on your pet’s risk of exposure and do not make general recommendations for all pets.  If your pet swims regularly in outdoor lakes or ponds, then its risk is much higher than a dog that spends its time primarily indoors.   If you travel out of Colorado with your pet, it is important to consider the mosquito population where you are going.

We will help guide you to make the best decision regarding prevention, and if necessary, treatment of heartworm disease for your pet.