Heart Disease in Dogs: Causes, Symptoms, Testing & Treatment
Heart disease affects roughly 10% of all dogs, rising to ~35% of dogs older than 13 years. Most cases develop with age. Of these, approximately 75% are mitral valve disease (MVD), 10% are dilated cardiomyopathy (DCM), and the rest are other conditions (heartworm, congenital defects, etc.).
MVD is common in older Cavalier King Charles Spaniels.
Mitral Valve Disease (MVD)
Mitral Valve Disease occurs when a heart valve weakens, allowing blood to leak when the heart contracts. MVD is most common in older, small-breed dogs—about 30% of small-breed dogs over 10 years show signs. It often progresses slowly, giving us an opportunity to slow progression and improve quality and length of life.
Dilated Cardiomyopathy (DCM)
Boxer is a breed that is affected by DCM.
DCM affects the heart muscle itself and commonly shows up in middle-aged, large-breed dogs (Dobermans, Boxers, Great Danes, Newfoundlands, and Cocker Spaniels). A juvenile form can affect adolescent Portuguese Water Dogs. The heart muscle becomes stretched and weak, reducing pumping efficiency and often progressing faster than MVD.
Symptoms of Heart Disease
Symptoms usually appear when heart disease progresses toward congestive heart failure (CHF). Watch for:
- Weight loss
- Weakness
- Exercise intolerance
- Low body temperature or cold limbs
- Rapid or difficult breathing
- Wet cough
Testing & Treatment Recommendations by Stage
Stage A
Dogs at high risk but with normal hearts (e.g., healthy Cavalier King Charles Spaniels) should have annual exams to check for murmurs. No specific medication is required at this stage.
Stage B (Structural changes but no symptoms)
- Chest X-rays for baseline heart size.
- Annual blood pressure and baseline labs (CBC, chemistry, urinalysis).
- Echocardiogram is ideal for diagnosis and staging; if unavailable, proBNP blood test is a useful screen.
Home Monitoring
Check resting respiratory rate while your dog is sleeping. If it exceeds 30 breaths per minute (or >15 breaths per 30 seconds) for three consecutive days, contact your veterinarian. Keep a log of respiratory rates and activity changes.
Substage B1
No visible changes on X-rays or echo. Focus on weight and muscle mass, avoid excess calories, and continue periodic checks.
Substage B2
Evidence of heart enlargement on imaging. Starting Pimobendan (Vetmedin) in Stage B2 MVD delays CHF by an average of ~15 months. Monitor X-rays, blood pressure, and resting respiratory rate every 6 months.
Stage C (Current or previous CHF)
Requires chest X-rays, BP checks, and labs every 3–6 months. Many dogs benefit from a combination of medications (often called “Quad Therapy”): pimobendan, a loop diuretic (e.g., furosemide), ACE inhibitor (benazepril/enalapril), and spironolactone. Dietary changes include moderate sodium restriction, maintaining calories to preserve muscle, and considering omega-3s or supplements like taurine/l-carnitine where indicated.
Home Care
- Monitor appetite and body condition; seek care if appetite drops or weight falls.
- If resting respiratory rate >30–35 breaths/min for 3 days or new coughing/poor exercise tolerance, contact your vet.
Stage D
Advanced, life-threatening heart failure that often requires referral and advanced testing/treatment (higher drug doses, alternative diuretics such as torsemide). Evaluate quality of life carefully; humane euthanasia may be considered when comfort and normal activity can no longer be maintained.
Important Contacts
Additional Resources
- Client handouts on common medications and monitoring
- Optimizing nutrition for pets with heart disease (Tufts)
- Pet Health Network — general pet health articles