Dilated cardiomyopathy in dogs: symptoms, tests and treatment

Overview

Healthy heart muscle contracts and pushes blood into arteries carrying it to the tissues. In DCM, heart muscle cell numbers or function gradually decline. The enlarged ventricular wall may become thinner. All four heart chambers enlarge in some dogs.

During the occult stage, rhythm or pumping investigations can detect disease even if the dog exercises normally. Heart failure causing fluid accumulation in the lungs or body cavities is called congestive heart failure. The mitral valve lies between the left atrium and ventricle.

DCM is not usually a structural heart defect apparent at birth; muscle function deteriorates with age. The left atrium often enlarges alongside the left ventricle. Mitral regurgitation can therefore result from heart muscle disease even when the original change is in the ventricle rather than the valve.

Causes

Genetics affects disease risk in many breeds. Two genomic regions containing genes related to heart muscle function have been identified in Dobermann disease. One studied gene, PRKAA2, affects energy metabolism in heart muscle cells. The precise cause of heart muscle disease is not established in every affected dog.

Taurine deficiency can underlie heart muscle weakness in some dogs. Certain chemotherapy medicines can damage heart muscle and cause similar disease. Genetics, other diseases and dietary composition may act together in non-hereditary DCM. Assessing food's contribution also considers how well the dog can utilise nutrients.

Carnitine deficiency has been suspected to contribute to heart muscle disease in some Boxers. Certain viral infections can also damage heart muscle and cause DCM-like changes. A dietary link has been suspected in dogs eating both grain-free and grain-containing foods.

Risk factors

DCM is most common in large and giant breeds. Predisposed breeds include Dobermanns, Irish Wolfhounds and Great Danes. It also occurs in smaller breeds, such as Cocker Spaniels. Diagnosis is usually made in middle-aged or older dogs.

In Dobermanns, symptoms typically begin at six to nine years old. A European follow-up study of 412 Dobermanns found a cumulative prevalence of 58.2% using its own criteria.

In the youngest group of that study, DCM was found in 3.3% of Dobermanns aged at least one but under two years. It was found in 9.9% of dogs aged at least two but under four. The proportion was 12.5% in dogs aged at least four but under six. In those aged at least six but under eight, it was 43.6%. In dogs over eight years old, it was 44.1%.

Disease was equally common in males and females in that follow-up. Males showed ultrasound changes earlier than females. Females had more ventricular premature complexes in this study.

One breeding health database in northern Europe recorded 85 Dobermann deaths from heart disease between 2014 and 2024. Forty-eight reports specifically concerned DCM. Not every dog dying from heart muscle disease is reported to the register, so these figures describe reported deaths.

Typical symptoms

The occult stage can last for years before an owner notices a change. Sudden collapse may be the first visible sign of a serious arrhythmia.

• Tiring more quickly than usual on walks.
• Faster breathing at rest.
• Coughing if the lung circulation becomes congested.
• Weakness showing as reduced activity.
• A brief fainting episode.
• Weight loss if tissue blood supply is inadequate.
• Abdominal enlargement from fluid accumulation.

A dog struggling to breathe may stretch the neck forwards to get more air. They may breathe rapidly with the mouth open. A dog with laboured breathing may stand with the legs wider apart than usual.

Complications and consequences

With left-sided failure, fluid can accumulate in lung tissue, causing pulmonary oedema. Fluid may collect around the lungs and restrict their expansion. A serious ventricular arrhythmia can cause sudden death without previous visible symptoms. Giant breeds may develop atrial fibrillation, with an irregular atrial rhythm.

Circulatory regulation initially helps compensate for weakened pumping. As disease progresses, the same regulation can increase salt and water retention. The outlook is usually worse if heart failure is already present at diagnosis.

Diagnosis at the vet

Heart structure and pumping

A soft murmur may be heard during contraction. Absence of a murmur does not rule out heart muscle disease. The vet can feel the femoral artery to assess whether the pulse is weak. Echocardiography particularly measures left ventricular size and assesses contraction. Left ventricular volume can be estimated from ultrasound images using Simpson's method. Chest X-rays assess fluid within or around the lungs.

Ultrasound measurements are compared with reference values for the dog's size, weight and breed. Doppler ultrasound can also assess blood flow within the heart. X-rays can assess heart size too. Blood tests can look for other diseases affecting treatment planning.

ECG and 24-hour rhythm monitoring

An electrocardiogram, or ECG, identifies the type of arrhythmia. A Holter monitor records heart rhythm over 24 hours while the dog moves and rests normally. Intermittent arrhythmias in Dobermanns can be missed on a short ECG. In a Dobermann, more than 300 ventricular premature complexes in 24 hours meets the rhythm criterion for occult DCM. The criterion may also be met if two 24-hour recordings within a year each show 50–300 ventricular premature complexes. A Dobermann can meet the rhythm criterion despite a normal ultrasound result.

A short, five-minute resting ECG can be used as an additional test when prolonged recording is unavailable. Blood cardiac biomarkers such as troponin I or NT-proBNP can provide additional information.

Fewer than 50 isolated ventricular premature complexes per day can be considered within normal limits for a Dobermann, but even a smaller finding is interpreted alongside other investigations.

Treatment

Treatment before heart failure

Hereditary DCM cannot be cured, but treatment can control symptoms and slow progression. Medication supporting heart muscle contraction may be considered for a Dobermann during the occult stage. A randomised trial included 76 Dobermanns whose DCM was not yet causing heart failure symptoms. Median time to heart failure or sudden death was 718 days with pimobendan and 441 days with placebo. Median survival in the same study was 623 days in the treatment group and 466 days with placebo.

The study enrolled Dobermanns aged four to nine with asymptomatic heart enlargement confirmed by ultrasound. Dogs with atrial fibrillation or dangerous ventricular arrhythmias were excluded. No clear difference was found between groups in the proportions reaching heart failure or sudden death during the study.

Heart failure and arrhythmias

A dog struggling to breathe because of pulmonary oedema may need supplemental oxygen in hospital. Diuretics reduce fluid accumulated in the lungs. Medicines supporting circulation can reduce ventricular workload. Medication can also control arrhythmias when needed. Follow-up investigations check the response and assess whether medication needs changing.

The outlook in advanced heart failure is generally worse than during mild disease. When DCM causes heart failure and does not respond to taurine treatment, most dogs die within six months of diagnosis.

Diet-associated cases

If cardiac changes are nutrition-related, heart function may improve with veterinary treatment and dietary change. A follow-up study compared dogs with DCM, of which 51 ate non-traditional and nine ate traditional diets before a diet change. Heart function was reassessed three, six and nine months after the change. Dogs previously eating non-traditional diets showed a small but measurable improvement in ultrasound findings. The dogs with DCM did not have low blood taurine concentrations at baseline.

Most dogs in the dietary follow-up also received taurine. Median survival was 611 days in dogs previously eating non-traditional food and 161 days in the comparison group, but the difference was not statistically significant.

Prevention

Clinical screening of Dobermanns with echocardiography and Holter monitoring is recommended from three years old. An earlier age-group follow-up suggested starting at two years old. Screening is repeated annually because disease can develop after a normal result. Dogs with hereditary heart disease should not be bred.

Some Dobermann breeding screening programmes require echocardiography and an ECG for a cardiac assessment. Under these programmes, the dog must be free of DCM on the breeding examination. The assessment is valid for 12 months. One Dobermann outcrossing project aims to broaden genetic diversity and reduce heart disease risk.

In some official cardiac screening schemes, an A result means no evidence of the specified heart disease on the examination date. An inconclusive B result means monitoring or repeat examination is advisable. A C result means the findings suggest the heart disease named in the assessment.

Important for dog owners

Count breaths for a minute while your dog sleeps quietly or rests without panting. One chest rise and fall together count as one breath. A healthy dog's respiratory rate is usually 12–30 breaths per minute. An increase above a heart patient's usual rate may indicate fluid accumulating in the lungs.

Record respiratory rate, breathing effort and appetite changes for monitoring. Contact the vet if resting breathing is repeatedly faster. If your dog struggles to breathe, go straight to emergency care and call on the way if possible.

Compare measurements taken in calm conditions: heat can cause rapid panting without worsening heart disease. Laboured breathing may show as unusually strong rib movement with every breath.

Frequently asked questions

Can DCM be symptom-free?

Yes: heart changes can exist for years before symptoms appear. Echocardiography helps detect ventricular enlargement at this stage. In Dobermanns, prolonged ECG recording can reveal rhythm changes before ultrasound becomes abnormal.

Is a normal result when listening to the heart enough?

No: heart muscle disease does not always cause an audible murmur. Echocardiography can assess left ventricular size and pumping even without one. Holter monitoring looks for arrhythmias over 24 hours, detecting rhythm changes absent during a consultation.

Is grain-free food the cause?

Being grain-free alone does not establish a diet as the cause. Nutrition-related DCM may involve several factors acting together, such as dietary composition and other diseases. Diet changes are planned with the vet according to nutritional needs. A dietary link has also been suspected with grain-containing foods.

Can a genetic test replace heart examinations?

A genetic test does not replace ultrasound and rhythm monitoring in Dobermanns. Genetic tests assess inherited disease risk, whose magnitude is not yet precisely known. Heart examinations instead establish whether detectable changes in structure, pumping or rhythm are already present.

How does DCM affect life expectancy?

The outlook varies with breed and disease stage at detection. A dog already in heart failure at diagnosis generally has a worse outlook than a symptom-free dog. Treatment can relieve symptoms and prolong life.