Which organ is primarily affected by Dirofilaria immitis infection in cats?

Dirofilaria immitis, commonly known as heartworm, primarily infects the heart and pulmonary arteries in cats. While the name "heartworm" suggests a focus on the heart, the disease manifests significant impacts on the lungs due to the presence of these parasites. When heartworms develop in cats, they cause inflammation and damage to the pulmonary vascular system, leading to conditions such as pulmonary hypertension and respiratory distress.

In cats, the presence of adult heartworms can lead to a disease known as heartworm-associated respiratory disease (HARD), which primarily involves the lungs. Symptoms may include coughing, wheezing, and difficulty breathing, highlighting the severe impact on pulmonary health rather than just cardiac function.

While other organs such as the kidney and liver can be affected indirectly due to systemic effects of the infection, the lungs are notably the organ primarily impacted by Dirofilaria immitis in feline patients, making it the most relevant choice in this scenario.