Heart Murmurs in Dogs: Grading, Causes & When to Worry

Hearing that your dog has a heart murmur can be alarming, but understanding what it means is the first step toward keeping your furry companion healthy and happy. A heart murmur is not a disease itself — it is an abnormal sound detected during a veterinary examination that may indicate an underlying condition. Some murmurs are harmless and resolve on their own, while others signal serious cardiac issues that require ongoing management.

Whether your veterinarian just mentioned a murmur during a routine checkup or you are researching symptoms you have noticed at home, this comprehensive guide will walk you through everything you need to know about heart murmurs in dogs. From the grading system veterinarians use to identify severity, to the most common causes, symptoms, treatment options, and when you should be concerned, this article covers it all.

Disclaimer: This article is intended for informational purposes only and does not constitute veterinary advice. Always consult with a licensed veterinarian for diagnosis and treatment of your dog’s health conditions.

What Is a Heart Murmur in Dogs?

A heart murmur is an unusual swishing or whooshing sound heard between the normal “lub-dub” heartbeats when a veterinarian listens to your dog’s chest with a stethoscope. This sound is caused by turbulent blood flow within or around the heart. In a healthy heart, blood flows smoothly through the chambers and valves, producing the familiar rhythmic heartbeat sound. When something disrupts that smooth flow — whether it is a leaky valve, a narrowed passage, or an abnormal opening — turbulence occurs, and a murmur is produced.

Heart murmurs in dogs are surprisingly common. They can be detected in puppies, adult dogs, and senior dogs alike. Some murmurs are present from birth (congenital), while others develop over time (acquired). Importantly, not all murmurs are cause for immediate alarm. Innocent or physiologic murmurs, particularly in young puppies, may disappear as the dog matures without any intervention.

However, because a murmur can also be an early indicator of significant heart disease, it should never be ignored. A thorough veterinary evaluation is essential to determine the cause, severity, and appropriate course of action. If your dog has been diagnosed with a murmur, your vet may recommend further diagnostics such as an echocardiogram (ultrasound of the heart), chest X-rays, or an electrocardiogram (ECG) to get a clearer picture of your dog’s cardiac health.

For more general information on keeping your dog in top shape, explore our health and wellbeing resources for tips on nutrition, exercise, and preventive care.

How Heart Murmurs Are Graded in Dogs

Veterinarians use a standardized grading system to classify the intensity of a heart murmur. This scale ranges from Grade I to Grade VI and helps communicate the severity of the murmur to other veterinary professionals. It is important to understand that the grade of a murmur does not always directly correlate with the severity of the underlying heart disease. A low-grade murmur can sometimes be associated with significant cardiac pathology, while a louder murmur may be relatively benign.

Grade I: Barely Audible

This is the softest murmur and can be very difficult to detect. It may only be heard in a quiet room with careful listening and may not be audible every time the veterinarian examines your dog. Grade I murmurs are often discovered incidentally during routine wellness exams.

Grade II: Soft but Detectable

A Grade II murmur is soft but consistently audible with a stethoscope. It is localized to one area of the chest and is generally easy for an experienced veterinarian to identify. Many mild or innocent murmurs fall into this category.

Grade III: Moderately Loud

This murmur is clearly audible and may radiate to more than one area of the chest. Grade III murmurs are often associated with mild to moderate heart disease and typically warrant further investigation, especially if your dog is showing any clinical symptoms.

Grade IV: Loud

A Grade IV murmur is loud and easily heard on both sides of the chest. There is no palpable thrill (vibration) associated with this grade. Murmurs of this intensity are frequently linked to significant structural heart disease and should be thoroughly evaluated.

Grade V: Very Loud with Palpable Thrill

At Grade V, the murmur is so loud that a vibration, known as a thrill, can be felt by placing a hand on the dog’s chest wall. This is a strong indicator of serious cardiac abnormality and requires prompt and comprehensive veterinary assessment.

Grade VI: Extremely Loud

A Grade VI murmur is the most severe on the scale. It is extremely loud, can be heard with the stethoscope barely touching or even slightly off the chest wall, and is accompanied by a strong palpable thrill. Dogs with Grade VI murmurs almost always have significant underlying heart disease that requires immediate attention.

Your veterinarian will consider the murmur grade alongside other factors — including your dog’s age, breed, symptoms, and diagnostic test results — to develop a complete picture of your pet’s heart health. If you are curious about how regular checkups can catch issues early, read our guide on senior dog health checkups to learn why consistent veterinary visits matter.

Common Causes of Heart Murmurs in Dogs

Heart murmurs can arise from a wide variety of causes, ranging from completely benign to life-threatening. Understanding the potential causes can help you have a more informed conversation with your veterinarian about your dog’s diagnosis and prognosis.

Innocent or Physiologic Murmurs

Not all murmurs indicate disease. Innocent murmurs, sometimes called physiologic or flow murmurs, occur when blood flows more turbulently through a structurally normal heart. These are especially common in puppies and are often outgrown by the time the dog reaches six months of age. They are typically low-grade (Grade I or II) and do not cause any symptoms. Stress, excitement, fever, anemia, and rapid growth can also produce temporary physiologic murmurs in dogs of any age.

Degenerative Mitral Valve Disease (DMVD)

This is the single most common cause of heart murmurs in adult and senior dogs, particularly in small and medium-sized breeds such as Cavalier King Charles Spaniels, Dachshunds, Poodles, and Chihuahuas. DMVD occurs when the mitral valve, which separates the left atrium from the left ventricle, degenerates over time and becomes thickened and leaky. Blood flows backward into the atrium instead of being pumped forward efficiently, creating a characteristic murmur. DMVD is progressive and, in many cases, eventually leads to congestive heart failure if left unmanaged.

Dilated Cardiomyopathy (DCM)

DCM is a disease in which the heart muscle becomes thin and weak, causing the chambers to enlarge and the heart to lose its ability to pump blood effectively. It is more common in large and giant breeds such as Doberman Pinschers, Great Danes, Irish Wolfhounds, and Boxers. DCM can produce a murmur due to the resulting valve dysfunction as the heart stretches. This condition is serious and often progresses to heart failure or dangerous arrhythmias.

Congenital Heart Defects

Some dogs are born with structural heart abnormalities that cause murmurs from a very young age. Common congenital defects include patent ductus arteriosus (PDA), pulmonic stenosis, subaortic stenosis, and ventricular septal defects (VSD). These conditions vary in severity — some are mild and may never require treatment, while others can be life-threatening and may need surgical correction. Certain breeds are predisposed to specific congenital defects; for example, PDA is more common in German Shepherds and Pomeranians.

Other Causes

Several other conditions can produce heart murmurs in dogs, including:

• Hyperthyroidism: Although rare in dogs (more common in cats), an overactive thyroid can increase heart rate and blood flow turbulence, leading to a murmur.
• Heartworm disease: Severe heartworm infections can damage the heart and pulmonary arteries, causing murmurs and significant cardiac dysfunction.
• Anemia: A low red blood cell count reduces blood viscosity, which can create turbulent flow and a detectable murmur even in a healthy heart.
• Infective endocarditis: A bacterial infection of the heart valves can cause murmurs and is a serious, potentially fatal condition.
• Hypertension: High blood pressure can increase the workload on the heart and contribute to murmur development.

Preventive care plays a huge role in catching these issues early. Learn more about heartworm prevention in dogs to protect your pet from this dangerous parasite.

Symptoms to Watch For & Treatment Options

Many dogs with heart murmurs, especially those with low-grade or innocent murmurs, show no outward symptoms at all. The murmur may only be discovered during a routine veterinary exam. However, when a murmur is associated with underlying heart disease, a range of clinical signs may develop over time. Recognizing these symptoms early can make a significant difference in your dog’s quality of life and treatment outcomes.

Common Symptoms of Heart Disease in Dogs

• Coughing: A persistent, dry, hacking cough — especially at night or after exercise — is one of the most common signs of heart disease in dogs. It occurs when an enlarged heart presses on the airways or when fluid accumulates in the lungs.
• Exercise intolerance: If your once-active dog tires quickly, refuses to go on walks, or seems winded after minimal activity, it could be a sign that the heart is struggling to keep up with the body’s demands.
• Rapid or labored breathing: Breathing that is faster than normal (especially at rest) or visibly effortful can indicate fluid buildup in the lungs, a hallmark of congestive heart failure.
• Fainting or collapsing episodes: Syncope (fainting) occurs when the brain does not receive enough oxygen-rich blood. It is a serious symptom that warrants immediate veterinary attention.
• Abdominal swelling: Fluid accumulation in the abdomen (ascites) can occur with right-sided heart failure and may make your dog look pot-bellied.
• Loss of appetite & weight loss: Dogs with advancing heart disease often eat less and may lose weight or muscle mass, particularly along the spine and hindquarters.
• Restlessness or difficulty sleeping: Dogs with heart disease may have trouble getting comfortable, preferring to sleep with their head elevated or sitting up rather than lying flat.
• Blue or gray gums: A bluish tint to the gums or tongue (cyanosis) indicates poor oxygenation and is a medical emergency.

Treatment Options for Heart Murmurs in Dogs

The treatment approach depends entirely on the underlying cause and severity of the condition producing the murmur. There is no single treatment for “a heart murmur” because the murmur itself is just a symptom, not a diagnosis.

Monitoring and observation: For innocent murmurs or very early-stage disease with no symptoms, your veterinarian may recommend regular rechecks — typically every six to twelve months — to monitor the murmur’s progression. This watchful waiting approach is common for puppies with physiologic murmurs and older dogs with early DMVD.

Medications: When heart disease is confirmed and begins to affect your dog’s heart function, a range of medications may be prescribed. These commonly include ACE inhibitors (such as enalapril or benazepril) to reduce the heart’s workload, diuretics (such as furosemide) to remove excess fluid from the lungs or abdomen, pimobendan to improve heart muscle contraction and dilate blood vessels, and beta-blockers or calcium channel blockers to manage arrhythmias or control heart rate. Your veterinarian will tailor the medication plan to your dog’s specific needs.

Dietary management: Nutrition plays a supportive role in managing heart disease. Low-sodium diets help reduce fluid retention, and supplements such as taurine, L-carnitine, omega-3 fatty acids, and Coenzyme Q10 may be recommended depending on the underlying condition. Some dogs with DCM linked to dietary factors may improve with a diet change, particularly if the condition is associated with grain-free or boutique diets.

Surgical intervention: Certain congenital heart defects, such as patent ductus arteriosus, can be corrected surgically or through minimally invasive catheter-based procedures. Early detection and intervention offer the best outcomes for these conditions.

Lifestyle adjustments: Dogs with heart disease may benefit from controlled, moderate exercise rather than intense activity. Keeping your dog at a healthy weight is critical, as excess body mass puts additional strain on the heart. For tips on maintaining your dog’s ideal weight, check out our guide on dog weight management.

When to See a Vet: Signs You Should Not Ignore

While not every heart murmur is an emergency, certain situations warrant prompt or immediate veterinary attention. Being proactive about your dog’s heart health can significantly improve outcomes and extend your pet’s life.

Schedule a veterinary appointment promptly if:

• Your dog has been diagnosed with a murmur and has not yet had a full cardiac workup, including an echocardiogram.
• The murmur was detected in a puppy and has not resolved by six months of age.
• You notice a new cough, especially one that persists for more than a few days or worsens at night.
• Your dog’s exercise tolerance has noticeably decreased.
• Your dog’s resting respiratory rate (breaths per minute while sleeping or fully relaxed) consistently exceeds 30 breaths per minute.
• Your dog has a known murmur and is due for a recheck — do not skip these appointments, even if your dog seems fine.

Seek emergency veterinary care immediately if:

• Your dog collapses or faints, even briefly.
• Your dog is struggling to breathe, breathing with an open mouth, or has extremely rapid breathing at rest.
• Your dog’s gums or tongue appear blue, gray, or pale white.
• Your dog has a distended, tight abdomen accompanied by lethargy or difficulty breathing.
• Your dog is coughing up pink, frothy fluid, which may indicate pulmonary edema (fluid in the lungs).

Early detection and consistent monitoring are the cornerstones of managing heart disease in dogs. Many dogs with heart murmurs and even diagnosed heart conditions live long, comfortable lives with proper veterinary care, appropriate medications, and attentive home management. The key is staying informed and working closely with your veterinarian every step of the way.

Regular wellness visits are essential for catching murmurs and other health issues before they become serious. Learn more about building a comprehensive preventive care plan for your dog to ensure a lifetime of health.

Frequently Asked Questions About Heart Murmurs in Dogs

Can a dog live a long life with a heart murmur?

Yes, many dogs live long, fulfilling lives after being diagnosed with a heart murmur. The prognosis depends heavily on the underlying cause and how early the condition is detected. Dogs with innocent or low-grade murmurs may never develop heart disease at all. Even dogs diagnosed with conditions like degenerative mitral valve disease can often live for years with proper medication, dietary management, and regular veterinary monitoring. The key is early detection and following your veterinarian’s recommendations closely.

Are heart murmurs in dogs hereditary?

Some causes of heart murmurs in dogs have a hereditary component. Degenerative mitral valve disease, for example, is strongly breed-associated, with Cavalier King Charles Spaniels being among the most affected breeds. Dilated cardiomyopathy also has genetic links in breeds like Doberman Pinschers and Irish Wolfhounds. Congenital heart defects such as subaortic stenosis and patent ductus arteriosus are known to run in certain breed lines. If you have a purebred dog from a breed predisposed to heart conditions, discuss screening options with your veterinarian, and always seek puppies from reputable breeders who perform cardiac health testing on their breeding stock.

How much does it cost to diagnose and treat a heart murmur in dogs?

The cost of diagnosing the cause of a heart murmur can vary widely depending on the tests required. A basic cardiac workup, including chest X-rays and an electrocardiogram, may range from a few hundred dollars. An echocardiogram performed by a veterinary cardiologist typically adds several hundred dollars to the total. Ongoing treatment costs depend on the medications prescribed and the frequency of follow-up visits. Monthly medication costs for managed heart disease can range from moderate to significant, depending on your dog’s size and the number of drugs required. Pet insurance can help offset these expenses, particularly if enrolled before a diagnosis is made.

Can diet or supplements help a dog with a heart murmur?

While diet alone cannot cure a heart murmur or reverse structural heart disease, proper nutrition plays an important supportive role. A balanced, appropriate diet that maintains your dog at a healthy weight reduces the strain on the heart. Low-sodium diets are often recommended for dogs with advancing heart disease to help manage fluid retention. Supplements such as taurine, L-carnitine, omega-3 fatty acids (fish oil), and Coenzyme Q10 may benefit some dogs, particularly those with DCM or nutritional deficiencies. Always discuss any dietary changes or supplements with your veterinarian before starting them, as some can interact with heart medications or may not be appropriate for your dog’s specific condition.

What is the difference between a heart murmur and heart disease in dogs?

A heart murmur is simply an abnormal sound caused by turbulent blood flow within or near the heart. It is a clinical sign detected during a physical exam, not a diagnosis in itself. Heart disease, on the other hand, refers to an actual structural or functional abnormality of the heart — such as a degenerating valve, weakened heart muscle, or congenital defect. A murmur can be a clue that heart disease is present, but not all murmurs are caused by heart disease (innocent murmurs are a prime example), and not all heart disease produces a murmur. This is why further diagnostic testing, such as an echocardiogram, is so important when a murmur is detected — it allows the veterinarian to see the heart’s structure and function directly and determine whether true heart disease exists.