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PEER REVIEWED An Everyday Approach to Canine Degenerative Mitral Valve Disease Mark A. Oyama, DVM, Diplomate ACVIM (Cardiology) D egenerative mitral valve disease (DMVD) is a common canine cardiac disease; approximately 30% of dogs over age 10 possess the characteristic left-sided systolic murmur of DMVD and resulting mitral regurgitation (MR).1 DMVD is most common in small breeds, with some breeds being highly predisposed. For example, virtually all Cavalier King Charles spaniels will develop DMVD during the course of their lifetimes. Developing a standardized approach to patients with DMVD can help the clinician concentrate on the most important diagnos- tic aspects of disease as well as provide useful information about monitoring and prognosis. This overview will focus on the role of the physi- cal examination and thoracic radiographs and how information from these tests can aid in the everyday diagnosis and management of DMVD. DIAGNOSIS OF DMVD Diagnosis of DMVD is one of the easiest clinical aspects of the disease. A presumptive diagnosis can be made on the basis of patient signalment and physical examination, wherein the hall- mark finding is an adult small-breed dog with a left-sided systolic murmur. In these instances, it is reasonable to assume that the source of the murmur is MR and hence, DMVD is pres- ent. Once a diagnosis has been made, the next question is: what is the severity of DMVD? ASSESSING SEVERITY OF DMVD Pathophysiology As DMVD worsens, the valve leaflets degener- ate, resulting in worsening MR. The reduction in forward cardiac output triggers activation of several neurohormonal pathways, includ- ing the renin–angiotensin–aldosterone system and sympathetic nervous system. For instance, reduction in renal perfusion results in renin release from the macula densa, which results in downstream production of angiotensin II via angiotensin-converting enzyme (ACE). 22 Today's Veterinary Practice July/August 2012 Figure. Right lateral and dorsoventral radiographs from a 12-year- old male Maltese with DMVD, demonstrating progressive left heart enlargement. The lower row of radiographs were taken approxi- mately 12 months after the upper row. Based on the marked change in heart size over this period of time, the risk of future congestive heart failure was high and increased owner monitoring for early signs of heart failure was warranted. The owner began keeping a log of the dog's respiratory rate and effort and was instructed to con- tact the veterinarian if the rate began to increase above the baseline value. Recheck physical examination and radiographs in 3 months were recommended. Angiotensin II and its related molecule aldosterone act to conserve sodium and water and expand plasma volume. In this way, cardiac output is maintained and there is an increase in cardiac stroke volume and, over time, ventricular size. Thus, the degree of volume reten- tion and subsequent eccentric cardiac hypertrophy is a marker of MR severity.