Cats that roam and are outside more are a little more at risk of becoming infected with heartworm. It's much less than the risk of a dog. Even so, because heartworm disease is invariably fatal for a cat if it reaches maturity, prevention is paramount.

The heartworm cycle in a cat is when a mosquito bites the cat and injects a baby worm into the cat’s skin. These worms then migrate through the skin into the bloodstream, and they arrive at the lungs, and that's when all the damage is done. Months later, when the worms start arriving at the lungs, the cat develops an intense inflammatory reaction to destroy these worms before they continue to mature. The cat has these asthma-like symptoms—coughing, open mouth breathing, vomiting, and labored breathing in general.

No, all heartworms have to go into a mosquito for part of their life cycle before being transmitted to another animal.

It's a parasite that lives inside. A mosquito injects these worms into the body of the cat, and it migrates toward the lungs.

Cat heartworm is an internal parasite that causes significant lung damage. Cats become infected by being bit by mosquitoes.