Dog Signs of Heart Murmur - Causes, Diagnosis & When to See a Vet
> Disclaimer: This article is for informational purposes only and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult your veterinarian with questions about your dog's health.
Quick Summary
A heart murmur in dogs is an abnormal sound heard during the heartbeat, usually detected by a veterinarian with a stethoscope. Some murmurs are harmless "innocent" murmurs seen in puppies, while others signal underlying heart disease. Knowing the signs—including lethargy, coughing, exercise intolerance, and breathing difficulties—helps pet owners seek timely care and appropriate treatment.
What Does Signs of Heart Murmur Look Like in Dogs?
Many heart murmurs produce no visible signs at all. Your dog may act completely normal while a murmur is present. Often, the murmur is discovered during a routine wellness exam.
When signs do occur, they typically reflect reduced heart function or poor blood flow. You may notice:
- Lethargy or reduced energy — Your dog tires more quickly than usual
- Coughing, especially at night or after lying down
- Rapid or labored breathing — Panting at rest or with minimal activity
- Exercise intolerance — Avoiding walks, play, or collapsing after exertion
- Fainting or collapse (syncope) — Brief loss of consciousness
- Bluish or pale gums — Indicates poor oxygenation
- Distended abdomen — Fluid buildup from heart failure
- Reduced appetite and weight loss
Common Causes of Signs of Heart Murmur in Dogs
- Innocent (physiological) murmur — Common in fast-growing puppies, usually disappears by 6 months. No treatment needed. No accompanying symptoms; dog is otherwise healthy.
- Degenerative mitral valve disease (DMVD) — The most common cause in older small breeds. The mitral valve thickens and leaks. Susceptible breeds: Cavalier King Charles Spaniel, Chihuahua, Miniature Poodle, Dachshund. Signs: cough, exercise intolerance, eventually heart failure.
- Dilated cardiomyopathy (DCM) — Heart muscle weakens and chambers enlarge. Susceptible breeds: Doberman Pinscher, Great Dane, Irish Wolfhound, Boxer. Signs: weakness, collapse, arrhythmias, sudden death in some cases.
- Subaortic stenosis — Congenital narrowing below the aortic valve. Susceptible breeds: Boxer, Golden Retriever, German Shepherd, Newfoundland. Signs: fainting, exercise intolerance, heart failure in severe cases.
- Patent ductus arteriosus (PDA) — Congenital defect where a fetal blood vessel fails to close. Susceptible breeds: German Shepherd, Maltese, Poodle. Signs: rapid breathing, stunted growth, heart failure in puppies.
- Pulmonic stenosis — Congenital narrowing of the pulmonary valve. Susceptible breeds: English Bulldog, Chihuahua, Beagle. Signs: fainting, exercise intolerance, right-sided heart failure.
- Heartworm disease — Worms in the heart and vessels cause turbulence and damage. Signs: cough, weight loss, exercise intolerance, ascites.
- Anemia — Low red blood cell count creates "flow" murmurs from thin blood. Signs: pale gums, weakness, rapid heart rate.
- Hyperthyroidism (rare in dogs) — Increased metabolism can cause murmurs. More common in cats.
- Endocarditis — Bacterial infection of heart valves. Signs: fever, lethargy, lameness, heart failure.
When Is Signs of Heart Murmur an Emergency?
Seek emergency care if your dog shows:
- Collapse or fainting
- Severe difficulty breathing or blue/pale gums
- Sudden weakness or inability to stand
- Distended abdomen that develops quickly
- Severe, persistent cough that interferes with rest
How Veterinarians Diagnose the Cause
Your vet will start with a thorough history and physical exam, including listening carefully to the heart and lungs.
Key diagnostic steps:- Echocardiography (heart ultrasound) — The gold standard to see valve structure, chamber size, and blood flow
- Chest X-rays — Assess heart size and lung changes (fluid, congestion)
- Electrocardiogram (ECG) — Evaluates rhythm and detects arrhythmias
- Blood work — Heartworm test, kidney/liver function (for medication dosing), thyroid panel
- BNP/NT-proBNP — Blood marker that can indicate heart strain
Treatment Options
Treatment depends entirely on the underlying cause and severity.
Innocent murmurs: No treatment. Recheck to confirm resolution. Degenerative mitral valve disease: Medications such as pimobendan, ACE inhibitors, diuretics, and diet changes can slow progression and manage heart failure. Regular monitoring is essential. Dilated cardiomyopathy: Similar medications; some breeds benefit from taurine supplementation. Prognosis varies. Congenital defects (PDA, stenosis): Surgery or catheter-based procedures may correct or improve some defects, especially when done early. Heartworm disease: Adulticidal treatment plus strict rest; prevention is critical going forward. Anemia: Address the cause (bleeding, parasites, immune-mediated) and provide supportive care.Lifestyle changes—weight management, controlled exercise, low-sodium diets when indicated—support heart health.
Prevention Tips
- Annual wellness exams — Early murmur detection allows monitoring and intervention
- Heartworm prevention — Year-round prevention in endemic areas
- Breeder screening — Ask about congenital heart screening for at-risk breeds
- Healthy weight — Reduces strain on the heart
- Dental care — Bacteria from dental disease can contribute to endocarditis