Which of the following is typically an acquired cardiac defect in dogs?

• A. Mitral insufficiency
• B. Pulmonic stenosis
• C. Atrial septal defect
• D. Ventricular septal defect

Answer: (A)

In dogs, the most common acquired cardiac defect is mitral insufficiency due to degenerative mitral valve disease. This condition develops as the valve leaflets and supporting structures thicken and become redundant over time, so they do not close properly during systole. Blood leaks back from the left ventricle into the left atrium, causing a volume overload that leads to left atrial and ventricular enlargement and can progress to heart failure if not managed. This contrasts with the other conditions, which are typically present from birth as congenital defects: pulmonic stenosis is an outflow obstruction at the pulmonary valve, while atrial and ventricular septal defects are holes in the heart walls that are usually congenital. The acquired nature of mitral insufficiency, its common occurrence with aging and breed predispositions, and its characteristic progression and murmurs make it the best answer.