Pathology and prognosis of canine myxomatous mitral valve disease

Myxomatous mitral valve disease is common in small breed dogs. However, the natural history of the disease is variable, with some dogs experiencing rapid progression to congestive heart failure and cardiac‐related death, while other dogs have disease that never progresses to produce clinical signs. Treatment is recommended according to the stage of disease progression, so understanding how to make this assessment is important. This article reviews the pathology and natural history of myxomatous mitral valve disease, and provides details of the most commonly used disease staging system.