Dirofilaria immitis, commonly called the canine heartworm, also infects cats. Cats become infected only 5 - 20% of the times that dogs become infected. However, when they do acquire heartworms, cats react more severely to them. Because their hearts are so much smaller than those of the dog, just a few worms can cause a lot of damage in cats.
When they do show signs, they are so variable that they do not point specifically to heartworms. Signs can range from simple lethargy, loss of appetite, and coughing to vomiting blood, having difficulty breathing, and sudden death. An infected cat can appear normal an hour before death.
Heartworms are carried by mosquitos to the host cat. By reducing mosquito breeding grounds, we greatly decrease the opportunity for our cats to become infected. Primarily, this requires minimizing standing water in areas the cats visit.
There are no completely reliable tests for heartworms in cats, though they are working on it. We currently use radiography (X-rays), ultrasound of the heart and lungs, and blood tests. The treatment itself is often dangerous, the death of the heartworm itself can cause a heart attack within the cat. Sometimes a surgery is necessary. As with all health problems, be sure to consult your vet!
*very little info, up until a decade ago, or so, vets were told that cats were immune to heartworms