Heart Murmurs in Senior Dogs

A heart murmur detected during a routine senior check is common and does not automatically mean heart failure is imminent, but it does warrant investigation because the two leading causes in older dogs, degenerative mitral valve disease and dilated cardiomyopathy, have different progression rates and treatment windows. Grading and monitoring the murmur over time is central to deciding when to intervene.

What a Murmur Actually Represents

A murmur is the sound of turbulent blood flow, most often caused in older small-breed dogs by degenerative mitral valve disease, in which the valve leaflets thicken and no longer close completely, allowing blood to leak backward into the left atrium during each heartbeat. In larger breeds, dilated cardiomyopathy causing a weakened, enlarged heart muscle is a more common underlying cause.

As mitral valve leakage worsens, the left atrium enlarges to accommodate the regurgitant volume, eventually raising pressure in the pulmonary veins and leading to congestive heart failure with fluid accumulating in the lungs. This progression can take months to years, which is why grading and monitoring the murmur's trajectory matters more than a single snapshot finding.

Leading Causes in Senior Dogs

• A soft cough, particularly at night or after lying down for a period
• Reduced stamina on walks that were previously managed comfortably
• Faster breathing rate at rest, particularly noticeable while sleeping
• Episodes of weakness, fainting or brief collapse, especially with excitement
• A distended abdomen from fluid accumulation in more advanced right-sided disease

Resting respiratory rate, counted at home while the dog is asleep, is one of the most useful early warning tools available to owners of dogs with known heart disease; a sustained rate above 30 breaths per minute at rest warrants a same-week veterinary check.

Grading and Monitoring Over Time

Echocardiography remains the gold standard for characterising a murmur, measuring chamber size, valve leaflet appearance and estimating the degree of regurgitation, and distinguishes mitral valve disease from cardiomyopathy or congenital defects. Thoracic radiographs assess heart size relative to the chest cavity and check for early fluid accumulation in the lungs.

NT-proBNP blood testing, a biomarker released in response to cardiac stretch, can help indicate whether a murmur is associated with significant structural change and is useful for monitoring progression between echocardiograms in dogs not yet showing symptoms.

Diagnostic Tests Beyond Auscultation

Treatment timing has shifted in recent years, with evidence now supporting earlier intervention once specific heart enlargement thresholds are reached, rather than waiting for symptoms of failure.

• Pimobendan, started once echocardiographic criteria for heart enlargement are met
• ACE inhibitors such as benazepril to reduce workload on the heart
• Diuretics such as furosemide once fluid accumulation (congestive failure) develops
• Dietary sodium moderation alongside maintained adequate protein and calorie intake

Living With Early-Stage Heart Disease

Dogs with early-stage, asymptomatic valve disease generally continue normal daily activity, though very strenuous exercise is best moderated as disease progresses. Regular weight monitoring is useful since both unintended weight loss from cardiac cachexia and weight gain from reduced activity affect heart workload.

Owners managing a dog on heart medication should keep a consistent dosing schedule and avoid over-the-counter anti-inflammatory drugs without checking with the vet first, since some interact with ACE inhibitors and diuretics and can affect kidney function.

When to seek help urgently

• Laboured or open-mouth breathing at rest, indicating possible fluid in the lungs
• Collapse or fainting episodes, particularly if repeated within a short period
• A resting respiratory rate consistently above 40 breaths per minute
• Blue or grey-tinged gums indicating inadequate oxygenation

A murmur alone is not an emergency, but its underlying cause and severity should be characterised by your vet through imaging so that treatment can begin at the point where it does the most good.