Mitral Valve Disease in Dogs: Stages, Treatment, and More

Mitral valve disease in dogs is a progressive heart condition in which the valve between the heart’s left chambers thickens, weakens, and no longer closes properly, allowing blood to leak backward with every heartbeat. It is the most commonly diagnosed heart condition in dogs, especially in small and toy breeds as they age. Mitral valve disease in dogs develop is often first identified during a routine wellness exam, long before any symptoms appear at home, simply because your veterinarian happens to hear a new murmur through the stethoscope. At Veterinary Healthcare Associates in Winter Haven, FL, we know a new diagnosis can raise a lot of questions, so this guide walks through the causes, stages, treatment options, and outlook for the mitral valve disease dogs are commonly diagnosed with.

What Causes Mitral Valve Disease in Dogs?

The exact trigger behind mitral valve disease dogs develop is not fully understood, but veterinary researchers point to a degenerative process affecting the valve’s connective tissue over time. As dogs age, the mitral valve leaflets can thicken and become less flexible, a change officially called myxomatous degeneration. Several factors influence which mitral valve disease dogs go on to develop:

• Genetics: Certain breeds, particularly Cavalier King Charles Spaniels, Dachshunds, Chihuahuas, and other small breeds, face a much higher lifetime risk than large-breed dogs
• Age: The condition becomes increasingly common as dogs move into their senior years, since the valve tissue has had more time to degenerate
• Sex: Some studies note a slightly higher prevalence in male dogs, though the effect is far smaller than that of breed and age
• Valve stress: Ongoing mechanical stress on the valve, combined with subtle changes in its collagen structure, contributes to the progressive leakage seen in mitral valve disease dogs experience as they get older

Because so much of the risk is written into a dog’s genetics, veterinarians cannot point to a single lifestyle cause the way they might with some other conditions. Instead, the focus shifts toward early detection through regular auscultation, so that any changes are caught and monitored from the earliest possible stage.

Can Mitral Valve Disease Cause Heart Murmurs in Dogs?

Yes, a heart murmur is typically the first clinical sign that leads to a mitral valve disease diagnosis. When the valve leaks, blood flows backward in a turbulent pattern that your veterinarian can hear as a murmur through a stethoscope. The murmur associated with mitral valve disease in dogs is usually loudest on the left side of the chest, over the point where the mitral valve sits.

Murmur intensity often correlates loosely with disease severity, though imaging is needed to confirm exactly how much the valve is leaking and how the heart has responded. Not every murmur means significant disease is present, and not every case of mitral valve disease produces a murmur loud enough to detect in its earliest phase, which is one reason your veterinarian may recommend periodic rechecks even when a first exam sounds normal.

What Are the Stages of Mitral Valve Disease in Dogs?

Veterinary cardiologists classify mitral valve disease in dogs into stages, which helps guide monitoring and treatment decisions at each point in the disease’s progression.

• Stage A: Dogs at high genetic risk, such as Cavalier King Charles Spaniels, that have no current evidence of disease
• Stage B1: A murmur is present, but the heart has not yet enlarged on X-rays or echocardiogram
• Stage B2: A murmur is present along with measurable heart enlargement, though the dog shows no outward symptoms
• Stage C: The dog has developed clinical signs of heart failure, such as coughing or labored breathing, either currently or in the past
• Stage D: Advanced disease that no longer responds well to standard treatment protocols

This staging system helps our veterinary team decide when to start medication, how frequently to recheck imaging, and what to watch for at home as mitral valve disease in dogs progress through each stage.

How to Prevent Mitral Valve Disease in Dogs

Because the mitral valve disease dogs are genetically predisposed to develop is largely inherited, there is no guaranteed way to prevent it entirely, particularly in high-risk breeds. That said, a few habits support long-term heart health and may help catch changes early, giving our veterinary team the best possible head start if the disease does appear.

• Schedule routine wellness exams so your veterinarian can listen for a new murmur before symptoms develop
• Maintain a healthy body weight, since excess weight places additional strain on the heart
• Ask your veterinarian about baseline cardiac screening if you have a breed predisposed to the condition
• Keep up with parasite prevention, since heartworm disease can also affect heart function over time
• Mention any family history of heart disease to your veterinarian, since breeders often track this within their lines

Treating Mitral Valve Disease in Dogs

Treatment for the mitral valve disease dogs face depends heavily on which stage the disease has reached. Dogs in Stage A or B1 typically need nothing more than regular monitoring, since medication has not been shown to benefit dogs before the heart enlarges. Once a dog reaches Stage B2, veterinarians often introduce medication aimed at slowing heart enlargement and delaying the onset of clinical signs.

Advanced Treatment and Ongoing Monitoring

For dogs in Stage C, treatment becomes more involved, often combining multiple medications that manage fluid buildup, support heart function, and control blood pressure. Your veterinary team will tailor the specific combination and dosing to your dog’s individual response, adjusting as needed at follow-up visits. Diagnostic imaging, including echocardiograms and chest X-rays, plays an ongoing role in tracking how the mitral valve disease responds to treatment over time, allowing adjustments before symptoms have a chance to worsen significantly. Nutrition can also factor into a treatment plan, since some prescription cardiac diets are formulated to support heart function alongside medication. Your veterinarian will let you know whether a diet change makes sense for your dog’s specific stage and needs.

What Is the Life Expectancy for Dogs With Mitral Valve Disease?

Life expectancy for the mitral valve disease dogs are diagnosed with varies considerably depending on the stage at diagnosis and how quickly the disease progresses. Dogs identified in Stage B1 often live for years with a normal quality of life, since the disease can progress very slowly at this point. Even dogs that reach Stage B2 frequently enjoy a good quality of life for an extended period once appropriate monitoring begins. Dogs that progress to Stage C generally have a more variable outlook, though modern treatment protocols have meaningfully extended comfortable, good-quality time for many patients.

What Helps Dogs Do Well Long-Term

Individual factors, including breed, age at diagnosis, and how closely a family follows the recommended monitoring schedule, all influence how the mitral valve disease dogs are living with progresses over time. Consistency at home matters as much as the medical plan itself. Giving medications on schedule, keeping follow-up appointments, and reporting new symptoms promptly all give your veterinary team the information they need to adjust treatment before a dog’s condition declines significantly.

Partnering With Veterinary Healthcare Associates for Your Dog’s Heart Health

A mitral valve disease diagnosis is a lot to take in, but you are not navigating it alone. Our team at Veterinary Healthcare Associates in Winter Haven, FL uses monitoring and individualized treatment plans to support mitral valve disease dogs throughout every phase of the condition. Whether your dog was just diagnosed with an early murmur or is further along in the disease process, our veterinarians will explain exactly what stage your dog is in and what that means going forward. Consistent follow-up care gives mitral valve disease dogs the best chance at a long, comfortable life. Call us at (863) 324-3340 to schedule a cardiac evaluation for your dog today.