How does it affect my cat?

The name "heartworm disease" is a misnomer, as the disease mostly affects the lungs and not just the heart. Signs are often mistaken for feline asthma, allergic bronchitis or other respiratory diseases.

In the x-ray, the cats lungs appear congested as a result of heartworm infection.

X-ray image courtesy of Dr. Ray Dillon, Auburn University College of Veterinary Medicine.