A cardiology resident once described mitral valve disease in Cavalier King Charles Spaniels this way: "It's not a question of if — it's a question of when." That's an oversimplification, but not by much. Heart disease is so common in certain dog breeds that screening is built into their wellness care from middle age onward.
For other breeds, the conversation starts when a vet hears something at a routine annual exam. "I'm picking up a murmur" can be one of the most anxiety-inducing things a dog owner hears. Understanding what it means — and what it doesn't — starts with knowing the disease.
Mitral Valve Disease: The Most Common Heart Condition in Dogs
Mitral valve disease, also called myxomatous mitral valve disease (MMVD) or endocardiosis, is responsible for the majority of heart disease in dogs. The mitral valve sits between the left atrium and left ventricle. With this condition, the valve leaflets gradually thicken and degenerate, preventing them from closing completely. Each time the heart beats, some blood regurgitates backward into the atrium rather than being ejected forward.
The result: a murmur. The heart's turbulent, backward-flowing blood creates the whooshing sound your vet hears through a stethoscope. Early murmurs are soft and cause no symptoms. Over time, the regurgitation increases, the left atrium enlarges under the increased pressure, and eventually — sometimes years later — the heart can no longer compensate, and fluid starts accumulating in the lungs.
Who Gets MVD
Small and medium breeds are disproportionately affected. Cavalier King Charles Spaniels have a genetic predisposition so strong that virtually all develop audible murmurs by middle age. Dachshunds, Poodles, Maltese, Chihuahuas, and other small breeds are commonly affected. Large breeds develop MVD too, but less frequently and typically later in life.
Male dogs show a notably higher prevalence of MVD-associated murmurs than females in some epidemiological studies, though the difference is modest and both sexes are affected significantly.
MVD Staging
The American College of Veterinary Internal Medicine (ACVIM) has published staging guidelines for MVD that guide treatment decisions:
- Stage A: High-risk breed with no murmur yet. Routine screening recommended.
- Stage B1: Murmur present, but no cardiac enlargement and no symptoms.
- Stage B2: Murmur present with measurable cardiac enlargement (verified by echocardiography or radiograph measurements), but still no symptoms. This is the stage where pimobendan treatment is now initiated based on major clinical trial data.
- Stage C: Congestive heart failure — current or previous episode of fluid accumulation. Active treatment required.
- Stage D: Refractory heart failure not responding to standard therapy.
Understanding Heart Murmurs in Dogs
Murmur grading (1-6) reflects loudness only. A grade 3/6 murmur doesn't mean three times the disease of a grade 1/6. Echocardiography, not murmur grade, determines actual disease severity and guides treatment decisions.
Dilated Cardiomyopathy: When the Muscle Fails
Dilated cardiomyopathy (DCM) is a disease of the heart muscle itself. The myocardium weakens, the chambers dilate, and the heart's ability to contract effectively diminishes. Unlike MVD, where the problem starts with a valve, DCM is a primary muscle disease.
DCM predominantly affects large and giant breeds. Doberman Pinschers are the most heavily affected — longitudinal screening studies put cumulative prevalence at roughly 58%, with the disease climbing sharply after age 6 (already around 44% of dogs by 6-8 years old) when screened with echocardiography and Holter monitoring. Boxers, Great Danes, Irish Wolfhounds, Saint Bernards, Scottish Deerhounds, and American Cocker Spaniels are also commonly affected.
The Doberman Pinscher version is particularly concerning because of how early and rapidly it can progress. Many Dobermans have significant ECG abnormalities (ventricular premature contractions) and structural changes before any symptoms develop. Holter monitoring (24-hour ECG recording) is recommended for screening this breed starting around age 3-4 years.
For more detail on this specific condition, dilated cardiomyopathy in dogs addresses the DCM-diet debate and breed-specific nuances.
Congenital Heart Defects
Some dogs are born with cardiac abnormalities. The most common in dogs include:
- Patent ductus arteriosus (PDA): A fetal blood vessel fails to close after birth, creating abnormal blood flow. Correctable surgically or via catheter-based intervention.
- Pulmonic stenosis: Narrowing of the pulmonic valve obstructs flow from the right ventricle. Mild cases may need no intervention; severe cases can be treated with balloon valvuloplasty.
- Aortic/subaortic stenosis: Narrowing at or below the aortic valve; particularly common in Boxers, Newfoundlands, and Golden Retrievers.
Congenital defects are typically detected young, often at the first puppy examination.
Arrhythmias
Abnormal heart rhythms can accompany structural disease or occur independently. Boxers and English Bulldogs have a breed predisposition to arrhythmogenic right ventricular cardiomyopathy (ARVC), where the right ventricle is replaced by fatty and fibrous tissue. Atrial fibrillation is common in giant breeds with advanced DCM. German Shepherds have a known predisposition to certain ventricular arrhythmias. Management depends on arrhythmia type, associated structural disease, and clinical signs.
Recognizing Heart Disease Symptoms in Dogs
Early heart disease is often silent. The first sign many owners encounter is a murmur detected during a routine exam. Once disease progresses:
- Coughing — particularly soft, persistent cough that worsens at night or after rest; occurs when fluid accumulates around the airways
- Increased breathing rate at rest — a resting rate above 30 breaths per minute is significant
- Reduced exercise tolerance — tiring faster than previously on walks
- Decreased appetite and weight loss (cardiac cachexia) in advanced disease
- Abdominal distension from right-sided heart failure and fluid accumulation (ascites)
- Fainting or collapse during exertion or excitement — with arrhythmias or severe outflow obstruction
- Weak pulse, pale or blue gums in severe cases
Diagnosis
- Physical examination including cardiac auscultation and pulse quality assessment
- Chest radiographs to evaluate heart size and check for pulmonary edema
- Echocardiography — the definitive assessment for chamber dimensions, wall motion, valve structure, and ejection fraction
- ECG for rhythm assessment; Holter monitor for 24-hour arrhythmia surveillance
- Blood pressure measurement
- Blood work including NT-proBNP cardiac biomarker if indicated
Treatment
Treatment is stage-dependent.
Stage B1: Monitoring every 6-12 months, no medication typically indicated.
Stage B2: Pimobendan has been shown to delay onset of congestive heart failure in dogs meeting specific echocardiographic criteria. This is a meaningful shift from the previous watchful waiting approach.
Stage C/D: Full heart failure management — pimobendan, diuretics (furosemide), ACE inhibitors, additional agents as needed. Dietary sodium restriction. Activity modification. Regular rechecks.
The goal is never to pretend the heart is normal. It's to support what function remains, extend the compensated phase as long as possible, and maintain quality of life throughout. Understanding the full scope of pet heart health and cardiac care helps owners make informed decisions alongside their veterinary team.
When to see your vet: If your dog has a breed predisposition (small breed, or large breed like a Doberman or Boxer), ask your vet about baseline cardiac screening. Any new murmur warrants follow-up. Coughing, increased breathing rate, reduced exercise tolerance, or fainting always warrants prompt evaluation.
FAQ
Can a dog live a normal life with heart disease?
Many dogs with early or moderate heart disease live normal, active lives for years. Quality of life is the primary goal, and with appropriate management, most affected dogs maintain good comfort and activity levels well into the disease course.
How long can a dog live with congestive heart failure?
Median survival from the onset of congestive heart failure in dogs with MVD is typically 9-18 months with treatment, though individual dogs vary enormously. Some dogs, particularly with large-breed DCM, may have shorter survival; others with MVD in smaller breeds exceed those medians. Your cardiologist can give context specific to your dog's disease stage and response to treatment.
Is heart disease in dogs genetic?
For breeds with documented predispositions, yes — there is a clear genetic component. Cavalier breeders have access to health screening protocols (auscultation screening, echocardiography) to reduce the prevalence in future generations. For DCM in Dobermans, genetic testing for the PDK4 gene mutation is available, though it does not identify all at-risk dogs.
At what age should dogs be screened for heart disease?
For predisposed breeds, cardiac auscultation at every annual wellness visit is reasonable from adult age (1-2 years). Dedicated echocardiographic screening is recommended for high-risk breeds like Cavaliers starting around age 2-2.5 and for Dobermans starting around age 3-4. Your vet can advise on what's appropriate for your dog's breed and individual risk factors.