By Dial A Vet Veterinary Team
Heart disease is common in dogs, and in many cases it develops quietly for years before a dog shows any sign at all. A vet might first pick it up as a murmur at a routine check. Knowing which type of heart disease your dog has matters, because the outlook, the tests, and the timing of treatment differ a great deal between them. This page outlines the most common types. If your dog already has signs of failure, such as fast breathing at rest, read our pages on heart failure in dogs and congestive heart failure.
Key takeaways
- Degenerative mitral valve disease is the most common heart disease in dogs, especially in older small breeds such as Cavalier King Charles Spaniels, Chihuahuas, and Poodles.
- Dilated cardiomyopathy (DCM) affects the heart muscle and is seen more in large breeds such as Dobermanns, Great Danes, and Irish Wolfhounds.
- Some dogs are born with heart defects, and heartworm infection can also damage the heart and lungs.
- Heart disease does not always mean heart failure. Many dogs live comfortably for years with early disease.
- Breathing that is fast or laboured at rest, fainting, or a swollen belly needs prompt veterinary care.
Degenerative mitral valve disease
The mitral valve sits between the left atrium and left ventricle. In many older dogs the valve leaflets slowly thicken and stop sealing properly, so some blood leaks backwards with each beat. That leak is what a vet hears as a murmur. Over time the left side of the heart can enlarge. Some dogs never progress beyond a murmur; others eventually develop fluid on the lungs. Cavaliers are especially prone and can develop the disease at a younger age. Our page on heart murmurs in dogs explains what a murmur grade does and does not tell you.
The ACVIM consensus guidelines group mitral valve disease into stages, from dogs at risk with no changes (stage A) through to dogs with heart enlargement but no signs (stage B2) and dogs in heart failure (stages C and D). Staging guides when a vet may recommend medication, so tests such as chest X-rays and an echocardiogram are often suggested even when a dog seems well.
Dilated cardiomyopathy (DCM)
In DCM the heart muscle weakens and the chambers stretch, so the heart pumps less effectively. It is mostly a disease of large and giant breeds, and in Dobermanns it often comes with abnormal heart rhythms that can cause fainting or sudden death before other signs appear. Screening with an echocardiogram and a 24-hour rhythm recording (Holter monitor) is often recommended for at-risk breeds. Diet-associated DCM has also been investigated in dogs eating some grain-free or "boutique" diets, so your vet may ask detailed questions about food.
Congenital heart disease
Some puppies are born with heart defects. Examples include a patent ductus arteriosus (a blood vessel that should close after birth but stays open), narrowing of the outflow valves (pulmonic or subaortic stenosis), and holes between heart chambers. A loud murmur in a young puppy is the usual first clue. Some defects can be corrected surgically or with a minimally invasive procedure, so early referral to a cardiologist can change the outcome.
Heartworm disease
Heartworm is spread by mosquitoes and is present in parts of Australia, particularly warmer and coastal regions. Adult worms live in the vessels of the lungs and the heart, causing inflammation and strain on the right side of the heart. It is far easier to prevent than to treat. See heartworm disease in dogs for prevention options to discuss with your vet.
Other conditions
Abnormal heart rhythms (arrhythmias), fluid around the heart (pericardial effusion, sometimes linked to tumours), and infections of the heart valves are less common but can be serious. Fluid around the heart can cause sudden weakness and collapse.
Signs to watch for
- Breathing faster than usual while asleep or relaxed
- A cough, often at night or after exercise, in a dog with a known murmur
- Tiring quickly on walks, lagging behind, or reluctance to play
- Fainting or sudden collapse, sometimes with excitement
- A swollen belly, weight loss, or poor appetite
- Pale or bluish gums
Coughing has many causes that are not heart related, from kennel cough to airway problems. Your vet will help tell them apart.
When it is an emergency
Go to an emergency veterinary hospital immediately if your dog is struggling to breathe, breathing with an open mouth or extended neck while resting, has blue or grey gums, collapses or faints, or cannot settle and keeps changing position to breathe. These can be signs of fluid on the lungs or a dangerous rhythm problem, and oxygen and treatment may be needed within minutes to hours.
How vets diagnose and manage heart disease
Diagnosis usually starts with listening to the heart and lungs and checking pulse and gum colour. From there a vet may recommend chest X-rays, an echocardiogram (heart ultrasound), an ECG, blood pressure measurement, and blood tests, including a cardiac biomarker in some cases. Treatment depends entirely on the type and stage. Some dogs simply need monitoring. Others benefit from medication started before signs appear, and dogs in heart failure need a tailored plan that is adjusted over time. This is decided by your vet or a veterinary cardiologist, not at home.
Long-term care and prevention
- Keep up regular health checks, especially from middle age and in predisposed breeds.
- Use year-round heartworm prevention if your vet recommends it for your area.
- Keep your dog at a healthy weight and discuss diet choices with your vet.
- If your dog has a murmur, learn to count the sleeping breathing rate and keep a simple record.
- For breeding dogs, ask about breed-specific heart screening.
FAQ
Does a heart murmur mean my dog has heart failure?
No. A murmur means there is turbulent blood flow. Many dogs with murmurs feel completely well for years. Tests help your vet decide whether the heart is enlarged and whether treatment is worthwhile yet.
Can heart disease in dogs be cured?
Most acquired heart disease is managed rather than cured. Some congenital defects can be corrected with surgery or a catheter procedure, and heartworm can be treated, although prevention is much safer.
Is my dog's breed at higher risk?
Small breeds are more prone to mitral valve disease and large breeds to DCM, but any dog can be affected. Ask your vet whether screening suits your dog.
Talk with a vet
If your dog has a new murmur, a cough, or seems more tired than usual, our vets can talk through the signs with you by video and help you plan tests with your local clinic. Book a consult at dialavet.com. If your dog is struggling to breathe or has collapsed, go to an emergency vet hospital now.
References
- Keene BW, et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of Veterinary Internal Medicine, 2019.
- Merck Veterinary Manual. Heart Disease and Heart Failure in Dogs and Cats.
- American Heartworm Society. Canine Heartworm Guidelines.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If your pet is having trouble breathing or has collapsed, contact a veterinary hospital immediately.