What is the most common heart disease diagnosed in older, small-breed dogs?

• A. Aortic stenosis
• B. Myxomatous Mitral Valve Disease (MMVD/MMVR)
• C. Dilated cardiomyopathy
• D. Hypertrophic cardiomyopathy

Answer: (B)

In older small-breed dogs, a degenerative disease of the mitral valve, called myxomatous mitral valve disease, is by far the most common heart condition. Over time the valve leaflets and supporting structures become thickened and distorted, leading to mitral regurgitation. The resulting volume overload enlarges the left heart and can progress to left-sided congestive heart failure. This pattern is particularly prevalent in small breeds such as Cavalier King Charles Spaniels, Maltese, Pomeranians, and related dogs, making MMVD the typical cardiac diagnosis in this population as they age. Clinically you often hear a systolic murmur at the left heart base, and imaging may show enlargement of the left atrium and ventricle with a regurgitant jet on echocardiography. Treatment focuses on monitoring and managing symptoms to slow progression, with medications like those that reduce congestion and support heart function when needed. Other listed diseases are more commonly seen in different contexts—some are congenital or breed-related, some affect larger breeds more, and hypertrophic cardiomyopathy is primarily a condition recognized in cats rather than dogs.