Endocardiosis
Learn what the condition is, how it may be detected early, how it is treated or managed, and which breeds or species are linked to it.
Condition snapshot
A concise guide to the condition’s pattern, detection, management and urgency.
This snapshot is a general guide, not a diagnosis or treatment plan. New, severe or worsening signs require veterinary assessment.
About the condition
Endocardiosis, more commonly called myxomatous mitral valve disease, is a degenerative condition of the heart valves and is especially common in small and older dogs. The mitral valve between the left atrium and left ventricle is affected most often, although the tricuspid valve on the right side can also be involved. Cavalier King Charles Spaniels have a particularly strong breed predisposition and may develop disease at a younger age than many other dogs.
The valve leaflets gradually thicken and become distorted. They no longer close tightly when the heart contracts, allowing blood to leak backwards into the atrium. This regurgitation creates the characteristic heart murmur. Over time, the left atrium and ventricle enlarge to accommodate the extra volume. Many dogs remain free of symptoms for years despite a murmur.
When the heart can no longer compensate, pressure rises in the vessels of the lungs and fluid can leak into lung tissue, causing congestive heart failure. Owners may notice increased sleeping respiratory rate, coughing, reduced exercise tolerance, restlessness at night or difficulty breathing. Sudden fainting can occur in some dogs, and rupture of small supporting cords within the valve can cause abrupt deterioration.
The stage of disease matters because a dog with a soft murmur and no heart enlargement does not require the same treatment as a dog with significant enlargement or pulmonary oedema.
Endocardiosis is progressive and cannot be reversed by medication, but many dogs spend a long period in the preclinical stage. Careful monitoring allows treatment to begin when evidence shows it is likely to provide benefit.
The mitral valve is affected most often, although other valves can be involved, and the disease may remain clinically silent for years before the heart begins to enlarge or congestion develops.
Coughing alone is not specific because airway disease is also common in older small dogs.
Screening & Early Detection
Annual cardiac auscultation is the simplest screening method, particularly in small breeds and dogs with a known predisposition. In high-risk breeds such as Cavalier King Charles Spaniels, examinations from young adulthood can identify a murmur before the dog develops symptoms. The veterinarian records the murmur’s location, timing and intensity and checks pulse quality and rhythm.
Once a murmur is detected, echocardiography is the most useful test for confirming valve degeneration and measuring heart enlargement. Chest radiographs can assess overall heart size and the lungs, while blood pressure and cardiac biomarkers may provide additional information in selected cases. Staging is important because treatment recommendations change when enlargement reaches a defined threshold.
Owners can contribute valuable monitoring at home by counting the dog’s sleeping respiratory rate when fully relaxed. A persistent increase from that individual dog’s usual rate can be an early sign of developing congestion and should be discussed with a veterinarian.
Difficulty breathing, blue or grey gums, collapse or a sudden marked increase in respiratory effort requires urgent assessment. Regular screening aims to identify progression before a respiratory crisis rather than waiting for obvious heart failure.
Diagnosis and staging use auscultation, chest radiographs and echocardiography. Blood pressure and other cardiac tests may also be useful.
Treatment & Management
Treatment depends on the stage of myxomatous mitral valve disease. Dogs with a murmur but no meaningful heart enlargement may not need medication and are monitored periodically. Once echocardiography or radiographs show significant enlargement despite the absence of clinical heart failure, pimobendan is commonly prescribed because it can delay the onset of congestive signs in appropriately staged dogs.
When congestive heart failure develops, diuretic medication is used to remove excess fluid from the lungs. Pimobendan is continued, and additional heart medications may be added according to blood pressure, kidney function and the individual response. Oxygen and injectable medication can be required during an acute breathing crisis.
At home, owners should give medication consistently and monitor appetite, energy, coughing and sleeping respiratory rate. Kidney values and electrolytes are checked after starting or changing diuretics because treatment that removes excess fluid can also affect hydration and renal function. Exercise is usually kept moderate and self-limited rather than stopped completely in a stable dog.
There is no medication that makes a degenerated valve normal again. Surgical mitral-valve repair is available in a small number of highly specialised centres but is not routine. For most dogs, staged medical management provides good quality of life, often for a substantial period. Rapid breathing at rest, collapse or inability to settle comfortably should be treated as urgent signs of possible decompensation.
Breeds or species affected
Afghan hound
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American Cocker Spaniel
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Beagle
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Boston terrier
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Bull terrier
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Cavalier king charles spaniel
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Chihuahua
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Pug
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Dachshund
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German shepherd
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Great Dane
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Japanese Chin
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Maltese
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Miniature Poodle
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Miniature Schnauzer
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Pekingese
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Toy Poodle
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Schnauzer (miniature, standard)
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Yorkshire terrier
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