What is the most consistent radiographic feature of MMVR?

• A. Pulmonary edema
• B. Right atrial enlargement
• C. Cardiomegaly without LAE
• D. Left atrial enlargement

Answer: (D)

Left atrial enlargement is the most consistent radiographic feature because myxomatous mitral valve degeneration causes regurgitation that primarily overloads the left atrium with volume. Over time, this chronic volume load dilates the left atrium, which is why the heart silhouette on standard thoracic radiographs typically shows enlargement of the left-sided chamber. This LA enlargement often appears as an expanded left heart border and can even straighten the caudal cardiac silhouette. Pulmonary edema can occur if the dog develops congestive heart failure, but it isn’t present in all cases, and right atrial enlargement isn’t a typical feature since the disease originates on the left side. Cardiac enlargement without left atrial enlargement is less common for MMVR.