Myxomatous mitral valve disease (MMVD) is the most common cause of primary mitral regurgitation in humans and the most common cardiac disease in dogs. Many similarities have been described and, therefore, the dog is considered to be a suitable natural model for MMVD in humans. Accurate identification of incipient myocardial deterioration is crucial to optimally time interventional surgery. Nonetheless, this issue is still an object of controversy. In this respect, studies of left ventricular (LV) function in dogs with MMVD could potentially be useful. The present review compares the results obtained in echocardiographic studies of LV function in humans and dogs with MMVD. Although different study designs pose a limitation and results within the two species are not entirely concordant, it appears that LV function is better preserved in small-sized and medium-sized dogs than in humans. This may limit the usefulness of dogs as a model for LV function in MMVD.