• Heartworm larvae induce an intense inflammatory response in the blood vessels and tissues in the lungs.
• Once an adult worm dies, after 1-2 years, there is an additional intense inflammatory reaction resulting in acute lung injury.

I thought heartworm was mainly a dog's disease.

Heartworm disease is not just a canine disease. Heartworms affect cats differently than dogs, but the disease they cause is equally serious.