Which radiographic sign is most consistent with heartworm disease in dogs?

• A. Enlarged right heart and tortuous pulmonary vessels
• B. Left atrial enlargement
• C. Diffuse interstitial edema
• D. Pleural effusion

Answer: (D)

The key idea is that heartworm disease affects the lungs and right side of the heart, and radiographs are used to look for signs of pulmonary vascular change and right‑sided heart involvement. In advanced disease, you can see fluid in the chest (pleural effusion) due to congestion from right‑sided heart failure or caval syndrome, which can produce a clear, detectable radiographic finding. Among the given options, pleural effusion stands out as a visible consequence of the disease process on a thoracic radiograph, making it the most consistent sign to observe in this context. The other signs—enlarged right heart with tortuous pulmonary vessels, left atrial enlargement, and diffuse interstitial edema—can be caused by other conditions or may be less consistently present across cases. Thus, pleural effusion is the radiographic finding most reliably associated with clinically significant heartworm disease in this set.