Heart disease is common in dogs, progressive, and — critically — much better managed when caught before a dog is in crisis.
The good news is that there is one measurement you can take at home that is genuinely valuable, and most owners have never heard of it.
The resting respiratory rate
Count your dog’s chest movements while they are asleep, for thirty seconds, and double it.
Normal is roughly 10 to 30 breaths per minute.
A consistently rising resting rate, or a rate consistently above about 30, is one of the earliest signs of fluid accumulating in the lungs — and it appears before coughing and before any obvious distress.
For a dog already diagnosed with heart disease, cardiologists routinely ask owners to record this daily. It is the single most useful number you can bring to an appointment, and it frequently catches a deterioration days before anything else would.
Start now, while your dog is healthy, so you know their normal.
The two main diseases
Myxomatous mitral valve disease
The most common heart disease in dogs, accounting for the large majority of cases.
The mitral valve degenerates and stops sealing properly, so blood leaks backwards with each beat. The heart enlarges to compensate, and eventually pressure backs up into the lungs.
Who: small and medium breeds, particularly Cavalier King Charles Spaniels — where it is extremely common and often starts young — plus Dachshunds, Chihuahuas, Poodles, Yorkshire Terriers and King Charles Spaniels.
First sign: usually a heart murmur found at a routine check, often years before any symptoms.
Progression is slow in many dogs, and some never develop clinical signs. Others progress to congestive heart failure.
Dilated cardiomyopathy (DCM)
The heart muscle thins and weakens, the chambers enlarge, and the heart pumps poorly.
Who: large and giant breeds — Dobermans, Great Danes, Irish Wolfhounds, Boxers, Newfoundlands, Saint Bernards, Cocker Spaniels.
Often has a strong genetic component. It can also be associated with certain diets, which is the subject of ongoing investigation into grain-free and pulse-heavy foods.
DCM is frequently silent until it is advanced, and sudden death from arrhythmia is a real risk in some breeds — particularly Dobermans and Boxers. Screening in predisposed breeds, using echocardiography and sometimes Holter monitoring, is worthwhile.
Other causes
- Congenital defects — patent ductus arteriosus, pulmonic and aortic stenosis, septal defects, usually found in puppies
- Arrhythmias
- Pericardial effusion — fluid around the heart, often associated with tumours in older dogs
- Heartworm, where it is endemic
The signs
Early, and easy to dismiss:
- Reduced exercise tolerance — tiring sooner, lagging on walks
- An increased resting breathing rate
- Restlessness at night
- A soft cough, particularly at night or after lying down
Progressing:
- A persistent cough
- Faster or laboured breathing
- Reluctance to lie down flat, or sleeping propped up
- Reduced appetite and weight loss
- Abdominal swelling from fluid
- Fainting or collapse, particularly after excitement or exertion
- Pale or bluish gums
Emergency: difficulty breathing, blue or grey gums, collapse, or an inability to settle with rapid breathing.
Why the cough is misleading
A cough in an older small-breed dog is very often assumed to be a lingering infection. In practice it is frequently heart disease — an enlarged heart pressing on the airway, or fluid in the lungs.
The distinguishing features: a heart cough is typically soft and moist, worse at night and after lying down, and comes with reduced exercise tolerance.
A cough lasting more than a couple of weeks deserves a proper workup rather than another course of something empirical.
Diagnosis
- Auscultation — listening for a murmur or arrhythmia. Usually the first clue
- Chest X-rays — heart size, lung fluid
- Echocardiogram — ultrasound, which is the definitive test for structure and function
- ECG for rhythm disturbances
- Blood tests, including cardiac biomarkers such as NT-proBNP
- Blood pressure
A murmur alone does not tell you much — murmurs are graded, and grade does not correlate reliably with severity. An echocardiogram is what establishes what is actually happening.
Treatment
Depends entirely on the disease and the stage.
For mitral valve disease, there is now good evidence that starting a specific medication at the point where the heart has begun to enlarge — before any symptoms — delays the onset of heart failure substantially. That is the clearest argument for monitoring rather than waiting.
For congestive heart failure, treatment typically combines several medications and is highly effective at restoring quality of life.
Dietary management, including sodium moderation and often omega-3 supplementation, is part of the plan for many dogs.
Most dogs with well-managed heart disease live comfortably for a long time. This is not a diagnosis to despair at.
What owners can do
- Learn the resting breathing rate now, and record it weekly in a healthy dog, daily in a diagnosed one
- Keep them lean. Excess weight makes every cardiac and respiratory condition worse
- Exercise to tolerance — regular, moderate, guided by your vet. Not restricted entirely unless advised
- Annual check-ups, twice yearly from middle age. A murmur found at a routine visit is the whole point of routine visits
- Screen predisposed breeds. For Dobermans, Boxers, Cavaliers and other high-risk breeds, breed-specific screening schemes exist and are worth using
- Report changes promptly. Exercise tolerance, breathing rate, coughing, appetite
- Give medication exactly as prescribed, at consistent times, and never stop without discussing it
And if you are choosing a puppy
Ask about cardiac screening of the parents in breeds where schemes exist. In Cavaliers in particular, breeding protocols based on the age at which a murmur appears have been shown to shift the incidence in a population.
It is one of the few questions that genuinely changes the odds.
