Dogs With Heart Failure Have a Different Community of Gut Bacteria
Gut bacteria in dogs with heart failure look very different from those in healthy dogs, according to a new study published in BMC Veterinary Research. Researchers examined 78 dogs and found that the gut microbial communities—the trillions of tiny organisms living in your dog’s digestive system—were noticeably shifted in dogs with congestive heart failure. Specifically, a type of bacteria called Escherichia/Shigella was more common in sick dogs, while a bacteria called Megamonas was more abundant in healthy ones. The study also found differences in immune signals between the groups.
This research adds dogs to a growing list of species—including humans—where scientists are finding links between gut health and heart disease. While the findings are early and exploratory, they open the door to new questions about what’s happening in a sick dog’s gut, and whether that might one day become a focus for treatment.
Why the Gut–Heart Connection Matters for Dog Owners
You might be wondering: what does the stomach have to do with the heart? More than you’d think. The gut is home to billions of bacteria, fungi, and other microbes—together called the gut microbiome (think of it as a bustling city of microscopic neighbors living in your dog’s digestive tract). A healthy microbiome helps with digestion, but it also communicates with the immune system throughout the body—including pathways that can affect the heart and blood vessels.
In people with heart failure, researchers have found similar disruptions in gut bacteria—sometimes called gut dysbiosis (pronounced dis-BY-oh-sis), which just means the balance of bacteria has gone off-track. Scientists suspected the same might be happening in dogs, but the evidence has been limited. This study set out to fill that gap.
How the Study Was Set Up
The researchers recruited three groups of dogs:
- 38 dogs with congestive heart failure (CHF)—the most advanced stage of heart disease, where the heart can no longer pump blood efficiently and fluid may build up in the chest or abdomen
- 23 dogs with preclinical myxomatous mitral valve disease (MMVD)—a very common heart condition in dogs where a valve in the heart begins to leak; these dogs had the disease but hadn’t yet developed full heart failure
- 17 healthy control dogs—dogs with no known heart problems
All three groups had their gut bacteria analyzed through stool samples, which were sent for DNA testing to identify which bacterial species were present and in what amounts. The dogs also had their immune cell patterns measured—essentially, blood tests that look at how the body’s defense cells are behaving. Some dogs had levels of NT-proBNP checked as well—a blood marker that signals how much stress the heart is under, similar to how a check-engine light works in a car.
This type of study is called cross-sectional, meaning researchers took a snapshot in time rather than following dogs over months or years. That’s an important detail to keep in mind when interpreting what the results do and don’t tell us.
What the Researchers Found
A Different Bacterial Landscape in Sick Dogs
The most striking finding was a clear difference in gut bacteria between the groups. Dogs with congestive heart failure had higher levels of Escherichia/Shigella in their guts. This bacterial group is associated with inflammation and is generally considered less favorable when it becomes dominant—in both humans and animals.
Meanwhile, Megamonas—a type of bacteria more commonly found in healthy digestive environments—was more abundant in the healthy control dogs. Its lower presence in heart failure dogs suggests a shift away from a more balanced microbial community.
Immune Signals Were Also Different
Beyond the bacteria themselves, the immune cell patterns in dogs with heart failure were also different from those in healthy dogs. The immune system and the gut microbiome are in constant communication, so it’s not surprising that changes in one show up as changes in the other—though this study couldn’t determine which came first.
The researchers noted these differences as meaningful signals worth investigating further. They suggest the gut microbiome may play a role in how heart disease progresses in dogs, or at minimum, that heart disease changes what’s happening in the gut.
What This Means for Dog Owners
It’s Early Research—But It Points in an Interesting Direction
This is an exploratory study, which means its job is to look for patterns and raise questions—not to prove causes or recommend treatments. The findings don’t tell us that bad gut bacteria cause heart failure, or that fixing gut bacteria would reverse heart disease. It could be the other way around: heart failure might change the gut environment, altering which bacteria thrive.
Still, the consistency of the findings across 78 dogs is meaningful. It suggests a real relationship exists between gut health and canine heart disease—one that researchers will likely investigate more deeply.
Practical Steps to Discuss With Your Vet
If your dog has been diagnosed with heart disease—whether early-stage (MMVD) or advanced (congestive heart failure)—it’s worth having a conversation with your veterinarian about overall health and gut wellness. While the science isn’t yet at the point of recommending specific gut-targeted treatments for heart disease, here are some practical things to consider:
- Ask about diet—Nutrition plays a big role in gut bacteria balance. Your vet may have recommendations about the right diet for a dog with heart disease.
- Mention any digestive symptoms—If your heart-disease dog has frequent soft stools, changes in appetite, or digestive upset, let your vet know. It may be relevant to the bigger picture.
- Stay up to date on heart monitoring—Dogs with mitral valve disease, especially small breeds like Cavalier King Charles Spaniels, Dachshunds, and Chihuahuas, should have regular cardiac checkups to track disease progression.
When to Consult Your Veterinarian
Contact your vet promptly if your dog shows any of these signs, which may indicate worsening heart disease:
- Coughing, especially at night or after resting
- Faster or more labored breathing than usual
- Reduced energy or reluctance to exercise
- A swollen belly
- Fainting or collapsing episodes
- Loss of appetite or unexplained weight changes
If your dog is already on heart medications, do not change or stop them without veterinary guidance.
Study Limitations to Keep in Mind
Because this was a cross-sectional study, researchers cannot say whether changes in gut bacteria happen before heart failure, as a result of heart failure, or both. The study also didn’t follow the dogs over time to see how the microbiome changed as disease progressed. Future studies using longer follow-up periods and larger groups will be needed to understand the direction of this relationship. Additionally, as an exploratory study, replication in other dog populations will be important to confirm the findings.
The Bottom Line
A new study of 78 dogs found that gut bacteria in dogs with congestive heart failure are measurably different from those in healthy dogs. Dogs with heart failure had more Escherichia/Shigella—a less favorable bacteria—while healthy dogs had more Megamonas. Different immune signals were also observed. While this research can’t yet tell us whether gut bacteria changes cause heart disease or result from it, the findings are a meaningful step toward understanding the gut–heart connection in dogs.
For now, the most useful takeaway is this: heart health and gut health may be more connected than we once thought. Keeping your vet informed about your dog’s overall wellness—including digestive health—is always a smart move, especially if heart disease is already in the picture.
This article summarizes peer-reviewed research for educational purposes. Always consult with your veterinarian for personalized advice about your pet’s health and behavior.