Heart Disease in Dogs: Signs, Types, Stages and Treatment

Signs of Heart Disease in Dogs

Early heart disease often causes no signs at all; the first clue is usually a murmur your vet hears at a checkup.^13,1 As it progresses, watch for:^4,2,14

• Tiring easily on walks, lagging behind or not wanting to play
• Coughing, especially at night, when lying down or after exercise
• Faster breathing or breathing harder while resting or asleep
• Restlessness at night, or trouble getting comfortable
• Fainting or collapsing, especially with excitement or exercise
• A swollen belly from fluid buildup
• Weight and muscle loss, or a poor appetite

Many of these signs also happen with lung disease, airway collapse or simply age, so a vet exam is needed to tell them apart.¹ See dog heart disease symptoms and why dogs cough.

Types of Heart Disease in Dogs

• Mitral valve disease (MMVD): the mitral valve slowly thickens and leaks. It's the most common type by far, mainly in small and medium breeds, and usually starts in middle age.^1,3,13
• Dilated cardiomyopathy (DCM): the heart muscle weakens and the heart enlarges. It mainly affects large and giant breeds such as Dobermans, Great Danes, Boxers and Irish Wolfhounds.^15,16
• Arrhythmias: abnormal heart rhythms. Boxers get an inherited form (arrhythmogenic right ventricular cardiomyopathy) that can cause fainting or sudden death.⁶
• Congenital heart defects: present from birth and found in fewer than 1% of dogs. The most common are patent ductus arteriosus (PDA), subaortic stenosis and pulmonic stenosis.^17,18 PDA is one of the most common congenital defects in dogs and can usually be cured if it's closed early.^17,19,18
• Heartworm disease: worms spread by mosquitoes live in the heart and lung arteries. It's preventable with year-round medication.²⁰ See heartworms in dogs.
• Pericardial effusion: fluid builds up in the sac around the heart, most often from a tumor or an unknown cause, usually in middle-aged large breeds.⁸

Dog Breeds With Heart Problems

Mitral valve disease: Cavalier King Charles Spaniels have the highest risk, followed by King Charles Spaniels, Chihuahuas, Whippets, Poodles, Shih Tzus and Yorkshire Terriers.⁹ Heart murmur was the single most common disorder recorded in Cavaliers in UK practices, found in about 31% of them.²¹ About half of Cavaliers have a murmur by age 5.²² Males are affected more often than females.^1,9

DCM: Dobermans, Boxers, Great Danes, German Shepherds, Irish Wolfhounds, Scottish Deerhounds, Newfoundlands, Saint Bernards and Labrador Retrievers.^15,16 Specialists recommend Dobermans be screened every year from age 3 with an echocardiogram and a 24-hour heart rhythm (Holter) recording, because a single check isn't enough.¹²

Congenital defects: subaortic stenosis is most common in Boxers, Golden Retrievers, Rottweilers, German Shepherds and Newfoundlands; pulmonic stenosis in English Bulldogs, Boxers and Beagles.¹⁸

Stages of Heart Disease in Dogs

Vets use the American College of Veterinary Internal Medicine (ACVIM) stages, mainly for mitral valve disease:¹

• Stage A: at high risk (such as Cavaliers) but no heart abnormality yet.
• Stage B1: a murmur but no or only mild heart enlargement. No treatment is needed; recheck every 6 to 12 months.
• Stage B2: a murmur with enough heart enlargement on X-rays or ultrasound that starting pimobendan is recommended.
• Stage C: current or past signs of heart failure.
• Stage D: heart failure that no longer responds well to standard treatment.

How Vets Diagnose Heart Disease

• Listening with a stethoscope for a murmur or an abnormal rhythm. See heart murmurs in dogs.
• Chest X-rays to check heart size and look for fluid in the lungs. ACVIM recommends them for all dogs being evaluated.¹
• Echocardiogram (heart ultrasound), the best test to identify the cause of a murmur and measure the heart.^1,23 See enlarged heart in dogs.
• ECG or 24-hour Holter monitor for rhythm problems, especially in Boxers and Dobermans.^12,6
• NT-proBNP blood test, which helps show whether coughing or breathing problems are likely due to the heart.¹

You can also learn to check your dog's heart rate at home. Your vet may measure blood pressure, especially in older dogs and dogs with kidney or hormone disease.

Treatment of Heart Disease in Dogs

Treatment depends on the type and stage. There's no cure for acquired heart disease, but medication can delay heart failure, control symptoms and extend life.^1,14

• Stage B2 mitral valve disease: pimobendan, which helps the heart pump and widens blood vessels. In the EPIC trial it delayed heart failure or cardiac death from a median of 766 days to 1,228 days.^1,10 In the DELAY trial, spironolactone plus benazepril, compared with placebo, did not significantly delay heart failure.²⁴
• Heart failure (Stage C): usually a diuretic such as furosemide to clear fluid, pimobendan, an ACE inhibitor such as enalapril or benazepril, and often spironolactone.¹ See congestive heart failure in dogs and dog heart medicine.
• DCM in Dobermans: pimobendan started before symptoms delayed heart failure or sudden death from 441 to 718 days in the PROTECT trial.²⁵
• Congenital defects: PDA can often be closed by surgery or a catheter procedure, and pulmonic stenosis can be treated with balloon dilation.^18,19
• Arrhythmias: anti-arrhythmic drugs⁶ and, for some very slow rhythms, a pacemaker.

Never change or stop heart medications without your vet's advice, and don't give over-the-counter supplements or "natural diuretics" in place of prescribed treatment.

Diet and Exercise for Dogs With Heart Disease

• Sodium: mild restriction is suggested once the heart is enlarged, and more once heart failure develops. Avoid salty treats, deli meats, cheese and table scraps, and check that pill-pocket treats are low in salt.^1,26
• Keep muscle on: muscle loss is very common in heart failure, so dogs need enough protein and calories; low-protein diets aren't recommended unless there is severe kidney disease.²⁶
• Weight: keep your dog lean, at a body condition score of about 4 to 5 out of 9.²⁶
• Exercise: short, gentle walks suit most dogs with mild to moderate heart disease. Once a dog is in heart failure, avoid exhausting activities such as ball chasing and swimming, and stop if your dog breathes hard, lags or sits down.²⁷

Grain-Free Diets and DCM

In 2018 the FDA began investigating reports of DCM in dogs eating grain-free and pea- or lentil-heavy diets, many in breeds not normally prone to DCM. By late 2022 it had received 1,382 reports, but it hasn't established that these diets cause DCM and has stopped routine updates until there is meaningful new science.^28,29 In one study, dogs with DCM that were switched from these diets to traditional diets showed improved heart function over 9 months.³⁰ If your dog eats a grain-free or "boutique" diet, talk to your vet before changing foods.²⁸

Life Expectancy of Dogs With Heart Disease

It varies widely with the type and stage. Many dogs with early mitral valve disease (Stage B1) live normal lifespans, and most dogs with a leaky mitral valve never develop heart failure.^3,1 Once heart failure develops, survival is usually measured in months to a year or two. In the QUEST trial, dogs with heart failure treated with pimobendan reached the study endpoint (sudden death, euthanasia for heart disease or treatment failure) at a median of 267 days.^31,14 DCM generally has a worse outlook than valve disease once signs appear.^15,23

Track your dog's sleeping breathing rate. Healthy dogs average about 13 breaths a minute while asleep, and dogs with heart disease but no heart failure usually stay under 25 to 30.^32,33 A sleeping rate consistently above 30 is a common early warning of heart failure, so call your vet; if it's above 30 and your dog is also working hard to breathe, go now.^34,5,1

Frequently Asked Questions

What are the first signs of heart disease in dogs?

Often there are none; a vet hears a murmur first. Later signs include tiring easily, coughing (especially at night), faster breathing at rest, restlessness at night and fainting.

What dog breeds are prone to heart disease?

Small breeds such as Cavalier King Charles Spaniels, Chihuahuas, Poodles, Shih Tzus and Yorkshire Terriers are prone to mitral valve disease. Large breeds such as Dobermans, Boxers, Great Danes and Irish Wolfhounds are prone to dilated cardiomyopathy.

What are the stages of heart disease in dogs?

Vets use ACVIM stages A (at risk), B1 (murmur, little or no enlargement), B2 (enlarged heart, treatment usually started), C (heart failure) and D (heart failure that's hard to control).

How long can a dog live with heart disease?

It depends on the type and stage. Dogs with early valve disease often live normal lifespans. Once heart failure develops, many dogs live months to a year or more with treatment.

Are dogs in pain with heart disease?

Heart disease isn't usually painful, but advanced heart failure causes breathlessness, coughing and weakness that are distressing. Your vet can adjust medications to keep your dog comfortable.

Can heart disease in dogs be cured?

Acquired heart disease such as mitral valve disease can't be cured, but it can be managed for a long time. Some congenital defects, such as PDA, can be cured with surgery or a catheter procedure.

Do grain-free diets cause heart disease in dogs?

The FDA has investigated a possible link between grain-free, pea- or lentil-heavy diets and DCM, but hasn't proven a cause. Ask your vet whether your dog's diet is a concern.

Can heart disease in dogs be prevented?

Most inherited heart disease can't be prevented, but regular checkups catch it early, year-round heartworm prevention prevents heartworm disease, and screening helps at-risk breeds such as Dobermans.