Myxomatous mitral valve disease (MMVD) is the most common cause of heart disease in adult dogs, affecting millions of dogs worldwide. Small- and medium-sized dogs, especially Cavalier King Charles Spaniels, Dachshunds, Poodles, and Yorkshire Terriers, are predisposed to MMVD, suggesting that the disease has a genetic basis. MMVD typically progresses slowly, over several years, eventually resulting in heart failure in approximately half of affected dogs. Treatment in most cases is directed at reducing the impact and clinical signs of heart failure in an attempt to extend lifespan. There is need for better and more specific MMVD treatments, ideally to prevent the disease progressing to heart failure. Understanding why some dogs develop heart failure with MMVD and others do not, would make it easier to identify dogs who would benefit from closer monitoring or preventative treatment. Using a technology called ‘whole genome sequencing’ to study approximately 200 dogs, investigators have already identified 500 genetic variants that are more common in dogs or breeds with MMVD and/or heart failure. The research team will now study these variants in a larger number of dogs (240 dogs with MMVD and 240 dogs without MMVD) using archived clinical samples. Investigators plan to process this combined clinical and genetic information with machine learning to determine whether they can predict an individual dog’s risk of MMVD and heart failure. By the end of the study, investigators aim to use genetic information to identify dogs who would benefit from closer monitoring and early treatment of MMVD with appropriate medication, before they develop heart failure. Studying genetics will also help to understand more about MMVD itself, assisting with the design of better and more specific treatments to slow the progression of this common disease.