Understanding Canine Cardiac Murmurs: Clinical Presentation, Diagnostic Approach, and Management Insights

Owning a dog offers documented cardiovascular benefits to humans—lower resting heart rate, reduced blood pressure, and decreased cardiovascular disease risk. Yet pet owners often overlook their companion’s own cardiac wellness until a veterinarian detects something unusual during examination. A heart murmur in dogs represents one such finding that warrants careful attention, though not every murmur signals underlying pathology.

Defining Heart Murmurs and Their Origin

When veterinarians auscultate a dog’s thorax, they listen for two characteristic cardiac sounds: the “lub” and “dub” associated with valve closure. A heart murmur manifests as an abnormal, extraneous sound superimposed between these normal sounds—typically resulting from irregular blood flow patterns through the heart chambers or valves, according to the University of Missouri Veterinary Health Center.

Murmurs possess three diagnostic characteristics that veterinarians document:

Temporal Pattern: Whether the murmur persists continuously or appears intermittently throughout the cardiac cycle.

Intensity Grading: Whether the abnormality is readily discernible or requires focused listening to detect.

Anatomical Location: Which region of the heart produces the murmur.

Importantly, not all detected murmurs indicate cardiac disease. The Merck Veterinary Manual identifies “innocent murmurs” in healthy puppies under six months—transient findings that typically resolve without intervention.

Classification: Congenital Versus Acquired Presentation

According to Dr. Kimberly Nelsen, D.V.M., a veterinary medical director with IndeVets, heart murmurs in dogs fall into two categories:

Congenital murmurs exist from birth, representing structural or developmental variations present at whelping. Acquired murmurs develop progressively over the dog’s lifespan due to degenerative or systemic processes.

The underlying causes vary considerably. Breed predisposition plays a significant role—Chihuahuas and toy poodles demonstrate higher incidence rates. Systemic conditions such as anemia, severe infections including dental disease, mitral valve degeneration, septal defects, and chamber narrowing all contribute to murmur development. Dr. Nelsen emphasizes that “congenital and breed/age-related factors represent the most frequent etiologies by substantial margin.”

Clinical Manifestations: When Symptoms of Heart Murmur in Dogs Become Apparent

Many dogs with murmurs remain entirely asymptomatic. Dr. Preston Turano, D.V.M., spokesperson for Figo Pet Insurance, notes that veterinarians typically identify low-grade murmurs during routine wellness screening rather than through owner observation.

“Dogs with mild-to-moderate murmurs typically appear clinically normal in the home environment,” Dr. Nelsen explains. However, if cardiac compromise progresses toward frank heart disease, owners may observe:

Progressive exercise intolerance and rapid fatigue with minimal exertion. Respiratory difficulty or increased respiratory rate at rest or during activity. New or worsening cough, particularly during recumbency. Diminished appetite and weight loss. Lethargy with reduced activity levels and decreased stamina. Episodes of syncope or collapse.

The absence of these clinical indicators does not exclude murmur presence—many dogs live their entire lives with undetectable cardiac impairment.

Severity Grading and Diagnostic Evaluation

Veterinary cardiologists grade murmurs on a standardized scale ranging from 1 to 6, with higher grades indicating greater hemodynamic significance. This classification guides prognostication and therapeutic decision-making.

Physical examination via stethoscopy represents the initial diagnostic modality. When abnormal sounds become evident, referral to veterinary cardiology becomes indicated. Cardiologists employ multiple assessment techniques:

Comprehensive history and physical examination including oral, ocular, and vascular assessment alongside direct cardiac auscultation. Blood pressure monitoring to evaluate for hypertension, which may accompany renal, thyroid, or adrenal pathology. Resting electrocardiography (ECG) to characterize electrical activity and identify dysrhythmias. Prolonged ambulatory ECG recording (24-48 hours) capturing heart rate variability and ectopic beat frequency. Echocardiographic ultrasonography visualizing cardiac chambers, valve function, and associated vasculature. Cardiac catheterization in complex cases permitting direct hemodynamic assessment.

Financial Considerations and Insurance Coverage

Treatment costs fluctuate based on geographic location, murmur etiology and grade, and intervention intensity. Many low-grade murmurs require no specific therapy, while higher grades demand ongoing management.

Typical expenses include: veterinary exams ($40-$85, potentially needed quarterly or more frequently); cardiologist consultations ($400-$1,000 annually); daily medications for higher-grade murmurs ($50-$150 monthly); biannual to trimonthly laboratory work when medications are administered ($50-$350); and heart-specific dietary formulations (cost varies by brand).

Pet insurance coverage depends on individual policy terms and timing of diagnosis relative to enrollment. Dr. Dwight Alleyne, D.V.M., veterinary advisor at Better Pet, notes that most policies cover conditions developing post-enrollment, though congenital murmurs may face coverage limitations. Some insurers do provide pre-existing condition coverage with specific restrictions.

Prognosis and Life Expectancy

Longevity with a canine cardiac murmur depends substantially on murmur classification, associated pathology, and patient age. Dr. Grant Little, D.V.M., veterinary expert with JustAnswer, emphasizes this variability: “Older dogs may develop murmurs with no clinical expression before natural death from aging, while severe congenital murmurs can precipitate heart failure within 3-6 months without intervention.”

Dogs developing murmurs secondary to mitral valve disease demonstrate improved prognosis. “Early identification with minimal clinical manifestations allows most dogs to achieve long, satisfactory lifespans with appropriate monitoring and medical management,” according to Dr. Turano.

Age-Related Prevalence and Breed Considerations

Cardiac murmurs occur with high frequency in geriatric canines, particularly small breeds. Progressive degenerative valve changes over decades constitute the primary mechanism, explains Dr. Alleyne. The Cornell University College of Veterinary Medicine confirms that valve disease—predominantly affecting the mitral valve—dominates the murmur presentation in aging small dogs. Larger breeds develop murmurs at increased rates through cardiomyopathic processes involving the cardiac musculature itself.

The symptoms of heart murmur in dogs, while often silent initially, require vigilant veterinary monitoring throughout a dog’s life to ensure optimal cardiac health and quality of life maintenance.