Heart disease is one of the most common causes of illness and death in older dogs. It can be present for months or years before clinical signs appear, and early detection through routine veterinary exams can significantly improve outcomes. The two most prevalent forms of canine heart disease are degenerative mitral valve disease (DMVD), which accounts for roughly 75% of all canine heart disease cases, and dilated cardiomyopathy (DCM). Both conditions can progress to congestive heart failure (CHF), a state in which the heart can no longer pump blood effectively enough to meet the body’s needs.
Overview
Degenerative Mitral Valve Disease (DMVD)
DMVD is a progressive condition in which the mitral valve — the valve between the left atrium and left ventricle — degenerates and begins to leak. This causes blood to flow backward into the left atrium (mitral regurgitation), eventually leading to chamber enlargement and, in advanced cases, congestive heart failure with fluid accumulation in the lungs (pulmonary edema). Small and medium breeds are most commonly affected, including Cavalier King Charles Spaniels, Dachshunds, Miniature Poodles, Chihuahuas, and Cocker Spaniels. DMVD is staged using the ACVIM (American College of Veterinary Internal Medicine) consensus system from Stage A through Stage D.
Dilated Cardiomyopathy (DCM)
DCM is characterized by weakening and dilation of the heart muscle, reducing the heart’s ability to contract effectively. Large and giant breeds are most commonly affected, including Doberman Pinschers, Great Danes, Irish Wolfhounds, and Boxers. DCM can also develop secondary to nutritional deficiencies, particularly taurine deficiency, which has been associated with certain grain-free diets.
Symptoms
Dogs in the early stages of heart disease often show no outward signs. As the disease progresses, the following symptoms may develop. Contact your veterinarian promptly if you observe any of these:
- Coughing, especially at night or when resting
- Exercise intolerance or reluctance to play
- Rapid or labored breathing (increased respiratory rate at rest)
- Fainting or collapse episodes (syncope)
- Abdominal distension due to fluid accumulation (ascites)
- Weight loss and muscle wasting
- Restlessness or difficulty settling at night
- Pale or bluish gums
- Decreased appetite in advanced stages
A resting respiratory rate consistently above 30 breaths per minute in a sleeping dog is a key early indicator of developing heart failure. Your veterinarian may ask you to monitor this at home.
Diagnosis
Your veterinarian may use several tools to diagnose and stage heart disease:
- Physical examination — A heart murmur is often the first clue. Murmurs are graded on a scale of I to VI based on intensity.
- Chest radiographs (X-rays) — Evaluate heart size, detect pulmonary edema, and assess for pleural effusion.
- Echocardiography (cardiac ultrasound) — The gold standard for characterizing the type and severity of heart disease. Measures chamber dimensions, valve function, and cardiac output.
- Electrocardiogram (ECG) — Identifies arrhythmias that may accompany structural heart disease.
- Blood pressure measurement — Assesses systemic blood pressure, which can be elevated or reduced in heart disease.
- Cardiac biomarkers — NT-proBNP and cardiac troponin I blood tests can help screen for heart disease and monitor progression.
Treatment & Medications
Treatment depends on the type of heart disease and the ACVIM stage. Your veterinarian or a veterinary cardiologist will tailor the treatment plan to your dog’s specific needs.
| Medication | Role | Key Notes |
|---|---|---|
| Pimobendan (Vetmedin) | Inodilator — strengthens heart contractions and dilates blood vessels | Cornerstone of CHF treatment. The EPIC trial demonstrated that pimobendan delays onset of CHF in dogs with preclinical DMVD (Stage B2). Given twice daily on an empty stomach. |
| Furosemide (Lasix) | Loop diuretic — removes excess fluid from the lungs and body | Essential for managing pulmonary edema in CHF. Dose is adjusted to the lowest effective level. Requires monitoring of kidney values and electrolytes. |
| Enalapril / Benazepril | ACE inhibitors — reduce afterload and slow cardiac remodeling | Commonly used alongside pimobendan and furosemide. May support kidney perfusion. |
| Spironolactone | Potassium-sparing diuretic and aldosterone antagonist | Often added to triple therapy (pimobendan + furosemide + ACE inhibitor) for additional benefit. |
| Atenolol / Diltiazem / Sotalol | Anti-arrhythmic medications | Used when significant arrhythmias are present, particularly in DCM. Choice of drug depends on the type of arrhythmia. |
Dietary and Supportive Care
- Moderate sodium restriction as recommended by your veterinarian
- Omega-3 fatty acid supplementation (fish oil) may help reduce cardiac inflammation
- Taurine and L-carnitine supplementation in cases of suspected nutritional DCM
- Weight management to reduce cardiac workload
- Activity modification based on disease severity
Monitoring
Dogs with heart disease require regular veterinary monitoring, which may include:
- Resting respiratory rate monitoring at home (target below 30 breaths per minute while sleeping)
- Periodic chest radiographs to assess heart size and fluid status
- Repeat echocardiography to track disease progression
- Blood work to monitor kidney function and electrolytes, especially in dogs on diuretics
- Blood pressure checks
Prognosis
Prognosis varies significantly depending on the type of heart disease, the stage at diagnosis, and the dog’s response to treatment:
- DMVD Stage B1 (murmur, no enlargement) — Many dogs live for years without progressing to heart failure. Regular monitoring is key.
- DMVD Stage B2 (murmur with cardiac enlargement) — Pimobendan has been shown to delay onset of CHF by approximately 15 months on average.
- Stage C (congestive heart failure) — With appropriate medical management, median survival times range from approximately 6 to 18 months, though some dogs do better.
- Stage D (refractory CHF) — Advanced disease that is difficult to control with standard medications. Prognosis is more guarded.
- DCM — Prognosis is generally more guarded than DMVD, particularly in Doberman Pinschers where the disease can progress rapidly.
Early detection and timely initiation of treatment offer the best chance for extending quality of life. Your veterinarian is the best resource for understanding your dog’s individual prognosis.
Frequently Asked Questions
How do I count my dog’s resting respiratory rate? Watch your dog while sleeping and count the number of chest rises in 15 seconds, then multiply by four. A rate consistently above 30 breaths per minute warrants contacting your veterinarian.
Can heart disease in dogs be prevented? Most forms of canine heart disease cannot be prevented, as they have genetic components. However, feeding a balanced diet (avoiding potentially risky grain-free formulations linked to DCM), maintaining a healthy weight, and scheduling regular veterinary check-ups can support heart health and enable early detection.
Is exercise safe for dogs with heart disease? Mild to moderate exercise is often still appropriate for dogs in early stages of heart disease, but your veterinarian should guide activity levels. Dogs in active heart failure should have exercise restricted until stabilized.
What is the EPIC trial? The EPIC (Evaluate Pimobendan In Cardiomegaly) trial was a landmark study that demonstrated pimobendan given to dogs with preclinical DMVD and cardiac enlargement delayed the onset of congestive heart failure by a median of approximately 15 months compared to placebo.
Should I change my dog’s diet after a heart disease diagnosis? Your veterinarian may recommend a cardiac-specific diet or moderate sodium restriction. Do not make dietary changes without veterinary guidance, as nutritional needs vary depending on the type and stage of heart disease.