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Dog Health- My Dog Has Heart disease (MMVD)? Understanding the most common Canine Heart Disease


Dog heart disease

By Dr. Ryan Chuang


Today, let’s talk about the most common heart disease in dogs: Myxomatous Mitral Valve Disease (MMVD).




1. What is Myxomatous Mitral Valve Disease (MMVD)?


The mitral valve is a structural valve located within the left side of the heart. Its primary function is to act as a one-way valve, ensuring that blood flows in the correct direction when the heart contracts.

When the mitral valve undergoes degeneration and proliferative changes, it causes valvular insufficiency (improper closing). This allows blood to regurgitate (leak backward) into the left atrium. Over time, the chronic impact of this volume overload causes the left atrium to gradually dilate and enlarge, increasing the pressure within the chamber. If the heart can no longer compensate for this pressure, it ultimately progresses to congestive heart failure.

MMVD is the most common heart disease in dogs, with a significantly higher prevalence in middle-aged to senior animals. While it is most frequently diagnosed in small-breed dogs, it can also occur in medium and large breeds.


2. What are the Symptoms of MMVD?


If a dog suffers from mitral valve disease, owners might initially notice a decrease in stamina or that the dog pants more easily. However, before the condition progresses to active heart failure, many owners do not notice any obvious discomfort or clinical signs.

  • Severe Regurgitation: When the backward blood leakage becomes severe, some owners may actually feel an abnormal vibration or turbulence (cardiac thrill) when touching the dog's chest.

  • Pulmonary Hypertension: If the dog concurrently develops severe high blood pressure in the lungs, symptoms may become much more pronounced, and fainting (syncope) episodes can occur.

  • Congestive Heart Failure: If the heart disease is left unmanaged and progresses to heart failure, fluid begins to leak out of the bloodstream and into the lung tissues, causing pulmonary edema (fluid in the lungs). At this stage, owners will typically observe lethargy, an increased resting respiratory rate, respiratory distress, hypoxia (oxygen deficiency), or a chronic cough.


3. How is MMVD Diagnosed?

If a veterinarian detects a cardiac murmur over the left side of the chest during a physical exam, they will immediately suspect mitral valve disease, taking into account the dog’s age and breed predispositions.

  • Thoracic Radiographs (X-rays): These allow us to evaluate the overall size and shape of the heart, inspect the pulmonary blood vessels, and assess the condition of the lungs to assist in staging.

  • Echocardiography (Heart Ultrasound): If we wish to precisely evaluate real-time cardiac function and determine the exact clinical severity of the mitral valve disease, an echocardiogram is the gold standard method to obtain detailed diagnostic data.


4. Does MMVD Require Treatment? What are the Treatment Options?


Because a degenerated mitral valve cannot revert back to its normal structure, every single heartbeat will continue to cause blood regurgitation, steadily increasing pressure and workload on the heart. With age and time, the heart condition will gradually deteriorate, eventually leading to heart failure.

  • Core Medication: If left atrial enlargement is confirmed during a cardiac evaluation, it is strongly recommended to initiate medical therapy to delay the onset of heart failure. The primary drug clinically proven to prolong the asymptomatic phase is Pimobendan (commonly known under brand names like Vetmedin or Cardisure). This remains the absolute foundation of MMVD management.

  • Adjunctive Therapies: Depending on individual staging, other cardiovascular medications such as Benazepril (ACE inhibitor).

  • Heart Failure Management: Once active heart failure or pulmonary edema develops, diuretics are heavily relied upon to alleviate fluid accumulation and reduce the workload on the heart. For unstable and complicated cases, other medication might need to be added into treatment.

  • Supplements: Omega-3 fatty acid supplementation has been clinically proven to provide clear cardiovascular support. Furthermore, studies show that dogs with MMVD can have deficiency of Vitamin D. Provided that blood calcium and phosphorus levels are strictly monitored, appropriate low-dose Vitamin D (Calcitriol) supplementation can be considered.


5. Frequently Asked Questions (FAQ)


Q: My dog was diagnosed with MMVD. Will they need to be on medication for life? Once an echocardiogram or X-ray confirms that the left atrium has enlarged, a dog will require lifelong, continuous treatment with Pimobendan to protect their heart function. Other concurrent heart medications will be adjusted based on their specific disease staging and clinical changes. Once cardiac medication has begun, never stop the medication or adjust the dosage yourselfwithout explicit instructions from your veterinarian.


Q: What should I closely monitor in my daily routine at home?

  • Dietary Management: Avoid feeding high-sodium or salty human foods. Many commercial pet treats on the market contain very high sodium levels; excessive intake can destabilize heart conditions or even trigger acute heart failure.

  • Hydration (Water Intake): If your dog is prescribed diuretics, you must ensure they have unrestricted access to fresh drinking water. Never restrict water intake out of fear of pulmonary edema. Doing so can cause acute dehydration, which severely impacts kidney function and causes clinical distress.

  • Exercise Modification: Moderate, low-impact exercise is actually highly beneficial for overall health. However, you must strictly avoid strenuous activities that cause your dog to pant excessively, cough, or become overly exhausted.

  • Resting Respiratory Rate (RRR): This is your most vital tool. Monitor your dog’s breathing rate when they are completely asleep or deeply resting. Normally, it should not exceed 30 to 35 breaths per minute. If you notice their sleeping respiratory rate is consistently elevated, please contact your vet immediately to check if an early recheck is needed.

  • Strict Adherence to Medications & Rechecks: Administer all veterinary medications exactly as prescribed and attend all scheduled follow-up evaluations. If you observe any subtle changes or discomfort, seek advice from the clinic immediately. Never alter the treatment plan independently.

  • General Demeanor & Appetite: Keep a close eye on their daily energy, appetite, or any gastrointestinal symptoms (such as vomiting or diarrhea), and report any abnormalities promptly.


The above article is authored by Dr. Ryan Chuang. All rights reserved.


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