Heart disease in dogs

Recognise the signs

• EARLY SIGNS: Cough — initially only after exercise or at night; caused by enlarged heart compressing airways or fluid in the lungs
• Exercise intolerance — tiring more quickly on walks, reluctance to play
• Reduced appetite or subtle weight loss
• Occasional brief fainting (syncope) — momentary loss of consciousness, often after excitement or exercise
• PROGRESSIVE SIGNS: Faster breathing at rest — count breaths while dog is sleeping or relaxed; normal is 15–30 breaths per minute; above 30 is a warning sign requiring same-day vet contact
• Increased breathing effort — belly moving more than usual, or nostrils flaring
• Persistent cough, including at night
• Pot-bellied appearance (ascites — fluid in abdomen from right-sided heart failure)
• ACUTE HEART FAILURE: Severe breathlessness — the dog cannot settle and is in obvious distress
• Blue or purple gums and tongue (cyanosis)
• Collapse or extreme weakness
• Coughing up pink frothy fluid (pulmonary oedema)

First aid steps

1. 1. If you suspect acute heart failure (severe breathlessness, blue gums, collapse): phone an emergency vet immediately and transport the dog to the vet without delay.
2. 2. Keep the dog as calm as possible — do not allow exercise or excitement.
3. 3. Do not lay the dog on its side; allow it to find a comfortable position (many dogs in heart failure prefer to sit upright or stand).
4. 4. Keep the environment cool and well-ventilated — open windows if safe; avoid hot rooms.
5. 5. If prescribed emergency diuretic medication (e.g., frusemide) and the vet has instructed you to give an additional dose in an emergency — do so as directed. Otherwise, do not give any medications without veterinary instruction.
6. 6. If the dog is on heart medications, bring the medication list and bottles with you to the vet.
7. 7. Count the resting respiratory rate (RRR) if the dog is calm enough: count breaths over 15 seconds and multiply by 4. Report this number to the vet.
8. 8. For dogs already diagnosed with heart disease: phone your vet or the cardiac monitoring service number if provided, as early phone advice may prevent an unnecessary emergency visit or guide appropriate action.

While transporting to the vet

• Keep the dog upright and supported — do not lay in a flat position.
• Maximise ventilation in the vehicle; keep the car cool.
• Minimise noise and stress.
• Phone ahead so the vet can prepare oxygen and diuretic medication for immediate administration.
• Drive smoothly — avoid heavy braking or sharp turns.
• Monitor gum colour continuously — blue or grey is critical.

When it can usually wait

• A heart murmur detected at a routine check in a dog with no other symptoms — this requires follow-up (often echocardiogram) but is not an emergency.
• Occasional mild coughing after exercise in a dog already under cardiac monitoring — mention at next scheduled appointment but phone vet if it becomes more frequent.
• Mild exercise intolerance alone with no respiratory symptoms — book a routine vet appointment.

Common causes

• Mitral Valve Disease (MVD) / Myxomatous Mitral Valve Disease (MMVD) — the most common heart disease in dogs; the mitral valve between the left atrium and ventricle degenerates and becomes leaky (regurgitation); predominantly affects small to medium breeds
• Dilated Cardiomyopathy (DCM) — the heart muscle weakens and the chambers enlarge; predominantly affects large and giant breeds; also associated in some studies with grain-free diets (taurine-related DCM)
• Tricuspid Valve Disease — similar to MVD but affecting the right-sided valve
• Arrhythmias — abnormal heart rhythms (e.g., atrial fibrillation) can develop secondary to structural disease
• Congenital heart defects — present from birth (patent ductus arteriosus, pulmonic stenosis, subaortic stenosis); often detected in young dogs
• Pericardial effusion — fluid around the heart, often due to tumour (haemangiosarcoma, mesothelioma)
• Endocarditis — bacterial infection of the heart valves

What the vet will need to know

• Current medications and doses, including Vetmedin, frusemide, ACE inhibitors
• Current resting respiratory rate and any trend over recent days
• Any recent change in cough frequency, exercise tolerance, or appetite
• Most recent echocardiogram findings and date
• Any recent fainting episodes — duration and circumstances
• Breed and weight
• Any abdominal swelling noticed?
• Time since last dose of cardiac medication

Aftercare

• Dogs with confirmed heart disease require lifelong medication and monitoring. Malacetic Otic ear cleaner is a veterinary ear cleanser that helps restore normal ear pH — useful for ongoing ear hygiene between vet checks.
• Vetmedin (pimobendan) — positive inotrope and vasodilator; started at pre-clinical stage in dogs with enlarged heart chambers (EPIC trial evidence).
• Frusemide (furosemide) — diuretic to reduce fluid accumulation; dose may need adjustment.
• ACE inhibitors (e.g., enalapril, benazepril) — reduce cardiac workload.
• Regular echocardiograms (typically every 6–12 months) to monitor disease progression.
• Monitor resting respiratory rate at home daily — record in a diary and contact vet if consistently above 30 breaths/min.
• Moderate, controlled exercise — short, gentle walks rather than high-intensity activity; avoid extremes of heat.
• Cardiac diets (reduced sodium) may be recommended in advanced disease.
• Maintain a healthy body weight — obesity significantly worsens cardiac function.

Prevention

• Annual veterinary health checks allow early detection of heart murmurs before clinical signs develop.
• For breeds predisposed to MVD: voluntary cardiac screening programmes (Cavalier King Charles Spaniel MVD Breeding Protocol — endorsed by CKCS Club UK) aim to reduce inheritance.
• For DCM: avoid grain-free diets with exotic protein sources in large breeds until the relationship with taurine deficiency is better understood; consult your vet.
• Control body weight in all breeds.
• BVA/KC health schemes and breed club cardiac screening protocols should be followed by responsible breeders.
• Resting respiratory rate monitoring in at-risk breeds — discuss a home monitoring plan with your vet.
• Treat dental disease — significant dental infection (bacteraemia) is linked to endocarditis.

Breed-specific notes

• Cavalier King Charles Spaniel — very high prevalence of MVD; virtually all are affected by age 10; early onset common; CKCS MVD Breeding Protocol exists to reduce prevalence.
• Dachshund, Chihuahua, Miniature Poodle, Miniature Schnauzer, Maltese — high prevalence of MVD.
• Dobermann Pinscher — very high prevalence of DCM; can die suddenly from arrhythmia even before other signs develop; annual Holter monitoring recommended.
• Irish Wolfhound, Great Dane, Boxer, Cocker Spaniel — significant DCM risk.
• Boxer — also prone to Boxer cardiomyopathy (arrhythmogenic right ventricular cardiomyopathy) causing sudden death.
• Labrador Retriever — possible taurine-deficient DCM, particularly on grain-free diets.

Frequently asked questions