Heart Murmurs In Dogs: Causes, Symptoms, And Treatment Guide

Heart murmurs in dogs are unusual sounds heard during a heartbeat, caused by turbulent blood flow through the heart or blood vessels. These can range from harmless “innocent” murmurs, often seen in young puppies, to serious indicators of underlying heart disease that require veterinary attention. Understanding the type, grade, and cause of a heart murmur is crucial for determining if it’s benign or pathological, guiding appropriate diagnosis and management to ensure your dog’s cardiac health.

What Is a Heart Murmur in Dogs?

A heart murmur is an abnormal sound detected when a veterinarian listens to a dog’s heart with a stethoscope. Normally, the heart produces a rhythmic “lub-dub” sound from valve closures and blood flow. A murmur disrupts this with whooshing or swishing noises due to blood flowing turbulently instead of smoothly. These sounds occur between heartbeats: systolic (between lub and dub) or diastolic (after dub).

Innocent murmurs are common in puppies and young dogs, often resolving as they mature, linked to rapid growth or high cardiac output. Pathological murmurs signal structural issues like valve problems or heart muscle disease, more prevalent in older dogs or specific breeds.

Heart Murmur Grades in Dogs

Veterinarians grade heart murmurs on a scale of 1 to 6 based on intensity, loudness, and ease of detection. Higher grades often correlate with more severe underlying issues, though grade alone doesn’t confirm pathology.

• Grade 1: Very faint, heard only after minutes of listening in quiet conditions.
• Grade 2: Soft but easily heard.
• Grade 3: Moderate, louder than Grade 2.
• Grade 4: Loud with a palpable thrill (vibration felt on the chest).
• Grade 5: Very loud with thrill, audible with stethoscope barely on the chest.
• Grade 6: Extremely loud, audible without direct chest contact; indicates severe disease.

Grades 1-2 are often innocent, especially in puppies under 6 months. Grades 3+ warrant further investigation, particularly if accompanied by symptoms.

Types of Heart Murmurs in Dogs

Heart murmurs are classified by timing in the cardiac cycle:

• Systolic Murmurs: Occur during heart contraction (most common). Causes include mitral/tricuspid regurgitation, pulmonic/aortic stenosis, ventricular septal defects.
• Diastolic Murmurs: During heart relaxation, rarer; often from aortic/pulmonic regurgitation or mitral stenosis.
• Continuous Murmurs: Throughout the cycle, e.g., patent ductus arteriosus (PDA).

Innocent murmurs mimic these but lack structural abnormalities, typically systolic and low-grade.

Causes of Heart Murmurs in Dogs

Causes divide into congenital (present at birth), acquired (develop later), and extracardiac (non-heart related).

Congenital Heart Defects

Genetic conditions dogs are born with, comprising about 10% of murmurs in young dogs. Common types:

• Pulmonic Stenosis: Narrowed pulmonary valve obstructing right ventricle outflow.
• Ventricular Septal Defect (VSD): Hole between ventricles allowing blood shunting.
• Subaortic Stenosis: Narrowing below aortic valve.
• Tricuspid Valve Dysplasia: Malformed tricuspid valve.
• Patent Ductus Arteriosus (PDA): Fetal vessel failing to close post-birth.

Breeds prone: Boxers, Bulldogs (subaortic stenosis); English Springer Spaniels (PDA).

Acquired Heart Disease

Most common in adults, especially small breeds (>8 years).

• Myxomatous Mitral Valve Disease (MMVD): Degenerative valve thickening/leaking; affects ~10% of dogs lifetime, prevalent in Cavalier King Charles Spaniels, Chihuahua, Pomeranians.
• Dilated Cardiomyopathy (DCM): Heart muscle weakens/enlarges; common in large breeds like Dobermans, Great Danes.

Other Causes

• Anemia/Hypoproteinemia: Thin blood flows turbulently.
• Infections (Endocarditis): Bacterial valve damage, often from dental disease.
• Heartworm Disease: Parasites damage heart/lungs.
• Hyperthyroidism, Stress/Excitement: Temporary flow changes.

Symptoms of Heart Murmurs in Dogs

Innocent murmurs are asymptomatic. Pathological ones may show:

• Coughing (especially nighttime).
• Difficulty breathing/rapid panting.
• Fatigue, reluctance to exercise.
• Fainting/syncope.
• Weak pulse, pale/blue gums.
• Fluid buildup (ascites, pulmonary edema).
• Weight loss, poor appetite.

Early stages often lack symptoms; murmurs detected on routine exams. Symptoms indicate heart failure needing urgent care.

How Are Heart Murmurs Diagnosed in Dogs?

Diagnosis starts with auscultation, then advanced tests:

• Echocardiogram (Cardiac Ultrasound): Gold standard; visualizes structure, function, blood flow by specialists.
• Chest X-rays: Assess heart size, lung fluid.
• Blood/Urine Tests: Check anemia, kidney/liver function.
• ECG (Electrocardiogram): Detects arrhythmias.
• Blood Pressure: Hypertension screening.

Referral to veterinary cardiologist recommended for grades 3+.

Treatment for Heart Murmurs in Dogs

Treatment targets underlying cause; innocent murmurs need none, just monitoring.

• Medications: ACE inhibitors (enalapril), diuretics (furosemide), pimobendan for heart failure; antibiotics for endocarditis.
• Diet/Lifestyle: Low-sodium diet, weight control, moderate exercise.
• Surgery: For congenital defects (PDA ligation, valve repairs).

Regular 6-month checkups with echo/X-rays for progression. Prognosis varies: MMVD managed years; severe DCM guarded.

Prognosis and When to Worry

Worry if grade 3+, symptoms present, or adult dog. Innocent murmurs resolve by 6-12 months. Pathological: early intervention improves life quality/years. Monitor weight, activity; seek immediate vet if coughing/fainting.

Prevention and Home Management

• Annual vet exams for early detection.
• Prevent heartworm monthly.
• Dental care to avoid endocarditis.
• Healthy weight, breed-appropriate exercise.
• Breeders screen for congenital defects.

Frequently Asked Questions (FAQs)

What causes a heart murmur in a puppy?

Innocent murmurs from growth; congenital defects if persistent. Monitor till 6 months.

Can heart murmurs be cured?

Depends on cause: congenital may need surgery; acquired managed lifelong.

Is a Grade 2 heart murmur serious?

Often innocent, but recheck; further tests if symptoms.

Can stress cause heart murmurs in dogs?

Temporary yes, but persistent needs evaluation.

How much does treating a dog heart murmur cost?

Varies: diagnostics $500-2000; meds $50-200/month; surgery $3000+.

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medha deb

 

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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