If you have recently returned from the vet and heard the words “heart murmur” - or they have specifically diagnosed “Degenerative Mitral Valve Disease (DMVD)”, you are likely feeling a mix of anxiety - and a strong desire to act. Let’s have a look at how diet and supplements can help.

DMVD is the most significant cardiovascular challenge in small-breed dogs, accounting for approximately 75% of all canine heart disease cases. So even without a definitive diagnosis of the heart murmur’s cause, its probably this disease that’s causing the trouble.

As a veterinary cardiologist, the most common questions I am asked revolve around nutrition and supplements. Owners want to know what they can do at home to support their dog’s cardiac health for as long as possible, as naturally as possible.

While modern pharmacology is our most powerful tool, targeted nutritional choices can influence the developement of the disease, especially in the early stages.

Chapter 1: The Reality of DMVD

To understand the disease, we must understand the valve. The mitral valve is a one-way door between the left atrium and the powerhouse of the heart, the left ventricle. This valve must slam shut roughly 120,000 times every single day, holding back the full force of systemic blood pressure. It makes the pumped blood go the right way, forwards, and not backwards.

In DMVD, the valve leaflets become thickened and “lumpy,” and start prolapsing backwards, preventing a tight seal. When the heart contracts, some blood leaks backward into the atrium. This high-pressure, high-velocity “whooshing” is the murmur your vet heard. We categorise the disease using the ACVIM Staging System:

• Stage B1: Asymptomatic dogs with a murmur but no evidence of cardiac remodelling (the heart is still a normal size).
• Stage B2: Asymptomatic dogs where the heart has begun to enlarge to cope with the leak. This is the stage where we typically initiate medications like Pimobendan.
• Stage C & D: Dogs with past or current signs of congestive heart failure (CHF).

Chapter 2: The Sodium Paradox and Nutritional Priorities

For decades, the reflexive advice for any heart patient was “low sodium, immediately.” Mainly borrowed from human research and not so relevant to dogs. However, modern veterinary science suggests a more nuanced approach.

The Problem with Early Salt Restriction

In the healthy heart, the kidneys meticulously regulate sodium. As DMVD progresses, the body may activate the Renin-Angiotensin-Aldosterone System (RAAS). If we impose severe sodium restriction ($<50 \text{ mg/100 kcal}$) too early (Stage B1 or early B2), the body perceives this as a loss of circulating volume. This triggers an aggressive “metabolic backlash” of RAAS activation, increasing aldosterone levels which are pro-fibrotic and pro-inflammatory, and potentially accelerating the very damage we want to prevent.

Remember: Severe sodium restriction in preclinical dogs is strongly discouraged.

Protein and the Threat of Cardiac Cachexia

The biggest nutritional threat to your dog isn’t salt, it’s Cardiac Cachexia. This is a syndrome where the failing heart “burns” through muscle mass, driven by inflammatory cytokines like TNF-$\alpha$ and IL-1$\beta$.

Dogs lose muscle mass faster than fat in heart failure. We recommend avoiding “senior” or “kidney” diets unless concurrent disease exists, as these are often restricted in protein to protect renal function. For a cardiac patient, a protein intake of less than $6 \text{ g/100 kcal}$ is associated with rapid lean tissue loss; we typically aim for $8$ to $10 \text{ g/100 kcal}$.

MMVD Stage	Sodium Target (mg/100 kcal)	Primary Nutritional Goal
Stage B1	80 - 100	Establish baseline; avoid high-salt human treats.
Stage B2	50 - 80	Mild restriction to support management of cardiomegaly.
Stage C/D	50 - 80 (bespoke <50)	Manage fluid retention while avoiding aggressive RAAS activation.

Overweight dogs

Of course, if your dog is overweight, it is usually a good idea to try to gently reduce this extra fat tissue. It will reduce the strain the heart is under during exercise.

Chapter 3: The Supplement Deep-Dive

In a market full of pseudo-science, we must look at the supplements that actually have peer-reviewed evidence behind them.

1. Omega-3 Fatty Acids (EPA and DHA)

If you only pick one supplement, make it high-quality marine oil. Omega-3s work by integrating into the cell membranes, replacing more pro-inflammatory fats.

• Reduction of Cytokines: Studies show fish oil reduces the production of the cytokines that drive muscle wasting.
• Arrhythmia Protection: Omega-3s help stabilise the electrical activity of cardiac cells, reducing the chance of irregular rhythms.
• Dosage: The clinical target is $40 \text{ mg/kg}$ of EPA and $25 \text{ to } 30 \text{ mg/kg}$ of DHA daily.

2. Coenzyme Q10 (Ubiquinol)

CoQ10 is an essential cofactor in mitochondrial energy production. While human heart failure patients often show depletion, the data in dogs is more specific.

• Recent Evidence: A randomized, double-blind trial (2022) showed that while CoQ10 significantly increased plasma levels, it did not significantly impact heart size or clinical progression in Stage B2 dogs.
• Advanced Stages: It may help reduce systemic inflammation in Stage C and D patients.
• Clinical Tip: If using it, look for Ubiquinol (the liquid form), as standard powders are poorly absorbed by dogs.

3. Medium-Chain Triglycerides (MCTs)

The failing heart suffers an “energy crisis” because it struggles to process long-chain fatty acids. MCTs (found in specialized diets like Purina CardioCare) offer a metabolic bypass, providing a rapid energy source for the heart cells.

• The CPB Study: Dogs with Stage B1/B2 DMVD fed a “cardiac protection blend” containing MCTs showed a 3% reduction in heart size over six months, compared to a 10% increase in the control group.

More information is likely needed, to be sure of these results, but there is maybe enough here to suggest looking into these diets for your pet.

4. The Effect of Diuretics on Electrolyte “Gatekeepers”

When dogs are on loop diuretics like Furosemide, they lose several important things in their urine, which can make them deficient. Depending on how high a dose of diuretics they are on, these things become ever more important:

• B-Vitamins, also known as thiamine, can become depleted. Supplements are easy to find and probably worth considering, there isn’t any easy way to test if they are running a deficiency.

• Potassium is what allows the heart muscle to fire correctly. If it gets too low (hypokalemia), your dog might seem weak, lethargic,
  or even collapse. Appetite can also be affected. Blood tests can determine levels and the possible need for supplementation.

• Magnesium: Think of magnesium as the “gatekeeper.” If magnesium is low (hypomagnesemia), the kidneys cannot retain potassium, no matter how much you supplement. Low magnesium is also a major driver of refractory arrhythmias.

• Caution: Never start potassium/magnesium supplements without your vet checking a blood panel, as excessive levels (hyperkalemia) can cause the heart to stop.

5. Taurine

And what about Taurine, and it’s cousin L-Carnitine. These are commonly discussed as a deficiency has long been associated with heart muscle weakening and ‘nutritional DCM’. But this is a very different disease to DMVD.

Unless your dog is on a special boutique or ‘custom’ diet, or is a breed prone to DCM, they likely don’t need it for degenerative mitral valve disease. It won’t hurt, and supplements are easy enough to find - usually a 500mg human taurine supplement. But its low down on the priority list.

And what about the dreaded ‘grain-free’ diet?

Grain-free diets are also sometimes mentioned as a cause of nutritional DCM. But this isn’t a direct link. Most commercially sold grain-free diets are not a problem, especially in the UK. These diets usually have lots of taurine and L-carnitine in them these days, it seems to be more of a historic issue. They are often marketed as a ‘healthier’ option, which is slightly doubtful. But don’t worry too much if that is what you currently feed your dog.

6. Do we need to worry about cholesterol?

And what about cholesterol? We go on about it all the time regarding our own heart health. But dogs just don’t seem to get the arterial damage and cholesterol build up that causes all the problems in our own coronary arteries. So it just isn’t a big issue in most dogs, thankfully. There are a few medical conditions, mainly endocrine ones, that can cause cholesterol levels to go excessively high, which your vet should be checking for in at risk situations.

Chapter 4: The “Treat” Minefield

The most common reason for a sudden heart failure crisis is “hidden salt” in medication treats. Dogs are significantly more sensitive to salt than we are. To put this in perspective, I use the Doggy Treat Translator :

Human Food Item	Dog Equivalent (Human Terms)	Clinical Risk Level
1 Standard Sausage	1 Pepperoni Pizza	Critical (Sodium/Nitrates)
30g Cheddar Cheese	2.5 Hamburgers	Critical (Sodium/Fat)
2 Slices Wafer Thin Ham	1 Can of Cola	High (Sodium/Preservatives)
1 Slice of Toast & Butter	3 Doughnuts	Moderate (Sodium/Fat)
1 Digestive Biscuit	1 Medium Portion of Fries	Moderate (Caloric Density)

Safe medication hiders: Use plain boiled chicken breast, unsalted peanut butter (Xylitol-free!), or fresh carrot sticks.

Chapter 5: Monitoring at Home (The SRR)

Beyond diet, your most powerful tool is the Sleeping Respiratory Rate (SRR). While your dog is in a deep, dreamless sleep, count their breaths for one minute (one “in and out” equals one breath).

• Normal: Should be under 30 breaths per minute.
• Early Warning: If the rate consistently creeps into the high 20s or suddenly jumps, call your vet immediately. This is the first sign of fluid building up in the lungs.

Today, technology like smart collars (such as the Maven) allows us to track these metrics automatically 24/7, providing objective data that can help us catch problems before they become emergencies.

Final Thoughts

DMVD is a journey, not a cliff edge. By focusing on high-quality protein, strategic sodium management, and evidence-based supplements like Omega-3s, we can help our dogs live full, joyful lives despite their diagnosis.

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References:

Druzhaeva N, Nemec Svete A, Tavčar-Kalcher G, Babič J, Ihan A, Pohar K, Krapež U, Domanjko Petrič A. (2022) Effects of Coenzyme Q10 Supplementation on Oxidative Stress Markers, Inflammatory Markers, Lymphocyte Subpopulations, and Clinical Status in Dogs with Myxomatous Mitral Valve Disease. Antioxidants (Basel). Jul 22;11(8):1427.

Laflamme DP. (2022) Key nutrients important in the management of canine myxomatous mitral valve disease and heart failure. J Am Vet Med Assoc. Oct 8;260(S3):S61-S70

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