In today's VETgirl online veterinary continuing education podcast, we discuss the high prevalence of myxomatous mitral valve disease (MMVD) in dogs, particularly in smaller breeds, as well as the wide variation in outcomes that occur as a result of this disease have stimulated discussion as what factors may impact these variable outcomes. Some dogs with MMVD will never develop clinical signs referable to their disease during their lifetime, while others will progress to outcomes such as congestive heart failure, pulmonary hypertension, or cardiac arrhythmias. Whether significant differences in clinical progression occur among breeds has not been extensively investigated outside of Cavalier King Charles Spaniels, Dachshunds, and Miniature Poodles.