Heart Disease in Dogs: Warning Signs, Stages and When It Is an Emergency

I know you may be reading this at night with your dog next to you, trying to decide whether to leave now. This is how I would sort it.

Go to an emergency veterinarian now for any of these, according to the American Animal Hospital Association and the Merck Veterinary Manual:

• Breathing hard while at rest, or visible effort with each breath.
• Gums that look blue, gray, white, or purple. AAHA says these colors can mean the blood is not carrying enough oxygen.
• Collapse.
• Severe weakness.

Call ahead while you drive if you can, and bring any medicine names you have. A swollen belly belongs in the "now or very soon" group. Fluid from heart failure can cause it, but AAHA notes that other emergencies can too, so it needs prompt veterinary assessment.

Here is the "soon" group. A cough that has started, that keeps going, or that is getting worse, a dog that tires on walks it used to enjoy, fast breathing while asleep, or weight loss all call for a vet appointment within the next day or two. Call your regular veterinarian, describe what you see, and ask how quickly they want to see your dog. If the breathing looks like effort at any point, skip the appointment and go to the emergency clinic. Breathing effort is an emergency whatever number you count.

If you need a clinic, our emergency vet directory and vet directory can help.

A lot of owners land here because a vet heard a murmur at a checkup. A murmur is a sound caused by turbulent blood flow, picked up with a stethoscope. It may come from valve disease, a defect present from birth, increased blood flow, or another condition. The ACVIM consensus guidelines treat a murmur as an abnormal sound, not a stage. By itself it does not show the cause, how severe things are, whether heart failure is present, or whether your dog needs a particular medicine.

Two things follow from that. A murmur needs a veterinary assessment, so do not wave it off. It also does not prove congestive heart failure, so you do not have to assume the worst. A louder murmur does not always mean worse disease either, because the MSD Veterinary Manual calls murmur intensity an imperfect indicator. A mild murmur may be less serious, but loudness is not a complete measure.

"Heart disease" is also a group of different problems:

• Myxomatous mitral valve disease (MMVD) is a degenerative disease of the mitral valve and the most common heart disease in dogs, especially older small dogs. ACVIM lists Cavalier King Charles Spaniels, Dachshunds, Miniature Poodles, and Toy Poodles among the predisposed breeds.
• Dilated cardiomyopathy (DCM) is a disease of the heart muscle, with enlargement and weaker contractions. It shows up most often in middle-aged or older large dogs, according to the Merck Veterinary Manual.
• Congenital defects are structural problems present from birth, such as a patent ductus arteriosus or a narrowed valve.
• Heartworm disease is a parasitic infection that can damage the lungs, the heart, and other organs. It is a separate disease from MMVD and DCM, and our heartworm article covers it.

Most of the stage talk below applies to MMVD, because that is the disease the staging system was written for.

Some dogs have no signs at all for a long time. When signs do appear, the Merck Veterinary Manual and AAHA describe things like these:

• A cough that persists, including coughing at night.
• Tiring on walks, or less stamina than before.
• Faster breathing while resting or asleep.
• Weakness or fainting.
• A swollen belly from fluid.
• Weight loss.
• Reluctance to move.
• Less appetite, in advanced illness.

None of these proves a heart problem. Each has other possible causes, which is why the vet visit matters. A cough is not automatically a heart cough, so a dog with a known murmur or heart disease should be seen when a cough starts, lasts, or gets worse, or when it comes with abnormal breathing, weakness, fainting, or lower appetite.

This is the one home measurement vets ask for most, and it takes a minute. Wait until your dog is asleep or resting quietly in a cool room. Watch the chest. One rise and fall is one breath. Count for a full minute, or count for 30 seconds and multiply by two. VCA describes 15 to 30 breaths per minute as normal for a resting or sleeping dog, and the Merck manual puts a normal sleeping rate under 30.

Do not hold your dog to a number from the internet. Ask your vet what rate is too high for your dog, then write down each count with the date. A rate that is high, or that keeps creeping up over several days, is a reason to call. A normal count does not rule out heart disease, because it helps with monitoring and does not replace an exam. Tufts Cummings School uses the same counting method for home monitoring.

For the appointment, bring the breathing log, a note of any coughing, fainting, appetite, and activity changes, your dog's medicine names, recent test results, and what your dog eats.

Staging is a vet's job and it rests on testing. According to the NC State veterinary hospital and ACVIM, the workup can include:

• A physical exam, with the vet listening to the heart and lungs.
• Chest X-rays, which show heart size and whether fluid is in the lungs.
• An echocardiogram, an ultrasound of the heart that shows its size and how it moves.
• An ECG, when a rhythm problem is suspected.
• Blood pressure, blood and urine tests.
• A heart blood marker such as NT-proBNP.

Which tests your dog needs depends on the signs and what the vet suspects, so you may not need all of them.

On cost, prices vary a lot by clinic and region, so ask for a written estimate before you agree to a workup. For a sense of scale, one 2025 to 2026 cost guide gives roughly $250 to $500 for a specialty cardiology consultation and basic assessment, and one 2024 cardiology price list shows $875 for a cardiology or echocardiogram service. Those are examples, not fee schedules. Echocardiography, X-rays, an ECG, lab work, hospital stays, or emergency care raise the bill, and the scope of any listed fee should be confirmed with the hospital. Our pet insurance article covers coverage and pre-existing conditions.

The 2019 ACVIM consensus guidelines sort mitral valve disease into stages labeled A, B1, B2, C and D. Here is what each means for you.

• Stage A: Your dog is at higher risk than average but has no structural change in the heart. No drug treatment is recommended for stage A alone. Regular veterinary checkups are the plan.
• Stage B1: The valve disease is there, but the heart has not enlarged enough to meet the B2 criteria, and your dog has never had signs of heart failure. ACVIM does not recommend drug or dietary treatment for B1 on its own. Your vet will suggest when to recheck, based on imaging.
• Stage B2: The disease is still preclinical, with no heart failure signs yet, but the left atrium and ventricle have clinically important enlargement. This is the stage where treatment may start.
• Stage C: Your dog has current or past signs of heart failure caused by the valve disease, and the disease is not classed as resistant to standard treatment.
• Stage D: Heart failure keeps causing signs even with standard treatment. The veterinary team looks at advanced adjustments and quality-of-life decisions, and a specialist reassessment is appropriate.

If your dog has a murmur and no signs, you are most likely in the early stages. Only the testing above can say which stage applies.

Treatment is set by your veterinarian based on the disease type and stage. I won't give amounts, because the amount and the plan are your vet's call, and they change with your dog's kidneys, rhythm, and response.

This is how treatment generally breaks down by stage:

• Stage A and B1: No drug treatment is recommended for stage A, and none for B1 solely because of the disease.
• Stage B2: The EPIC trial studied pimobendan in selected dogs with preclinical MMVD and an enlarged heart. In those dogs, the median time to the study's composite endpoint was 1,228 days with pimobendan and 766 days with placebo, a difference of roughly 15 months. The EPIC study applies to that studied group, so it does not describe every dog with a murmur or every kind of heart disease.
• Stage C: Treatment may include pimobendan, diuretics such as furosemide, ACE inhibitors, spironolactone, oxygen, hospitalization, and other measures, depending on whether the heart failure is sudden or ongoing.
• Stage D: Specialist reassessment, advanced treatment decisions, and an honest talk about quality of life.

The Merck Veterinary Manual says the goals of heart therapy include resolving signs, keeping resting breathing and heart rates from being raised, and keeping a good quality of life for the pet and the owner.

Use each medicine exactly as your vet prescribes it. Do not stop one, skip one, or change one because your dog seems better or worse. If a dose is missed, or your dog seems worse on a medicine, call the vet's office and ask what to do.

No. I would not try, and I would not buy a cough remedy to test the idea. A cough can come from heart failure, but it can also come from airway disease, infection, tracheal disease, or other causes, according to the Merck Veterinary Manual. Only an exam, and often X-rays, can sort out which one you have.

What I would do instead: note when the cough happens, whether it comes with fast breathing, and whether your dog seems tired or weak. Record a short video if you can. Count sleeping breaths. Then call your vet the same day, and go to an emergency clinic if the breathing looks like effort.

If you are comparing causes, our kennel cough article covers that infection, and our reverse sneezing article covers the short noisy episodes that come from the upper airway. A persistent cough or any breathing difficulty is a different matter, and it belongs with a vet.

Your vet sets the plan, and it will change over time. These are the points I'd raise at the visit.

Exercise. Activity should be individualized by your veterinarian. A dog with heart disease can often still walk, but the right amount depends on the stage and how your dog is doing. Do not force your dog to keep going when it tires, coughs, gets weak, faints, or breathes abnormally. Stop, let your dog rest, and tell your vet about it. Our exercise article covers general needs, and a dog with heart disease needs a plan your vet signs off on.

Weight. Keeping a healthy body condition matters, so ask your vet what weight to aim for.

Food and sodium. Diet and sodium advice depends on the stage, kidney function, medicines, appetite, and other conditions. So, ask what your dog should and should not eat, including treats, before you change anything. Do not make a major diet change or add supplements without veterinary guidance. Salty human foods are worth asking about by name. For the FDA's look at diet and DCM, see our grain-free dog food article.

Heat. AAHA lists existing heart disease as a heatstroke risk factor, and suspected heatstroke is an emergency. Keep your dog cool, walk early or late, and never leave your dog in a parked car. See AAHA's page on heatstroke in pets.

Travel and boarding. Pack the medicines, a copy of your dog's records, water, and a plan for rest and cool conditions. Know where the nearest emergency vet is before you leave. Tell any boarding provider about the heart condition and the medicine schedule. Our vet directory can help you find a clinic near where you are going.

For general aging care, senior dog care is a good companion read.

I wish I could give you one number. No single lifespan applies to every dog. Outlook depends on the disease, the stage, how your dog responds to treatment, complications, and other illness, according to ACVIM.

The numbers that exist come from studies of specific groups. In EPIC, selected stage B2 dogs with MMVD and an enlarged heart had a median all-cause survival of 1,059 days with pimobendan and 902 days with placebo. Those figures do not apply to all heart disease, all stages, or all dogs.

Dogs in stage C or D have a more variable outlook. It depends on the cause of the heart failure, how severe it is, how well treatment works, kidney function, rhythm problems, high blood pressure in the lungs, how often fluid returns, and other disease. A vet who knows your dog's tests can talk about what to expect for your dog.

Advanced or treatment-resistant disease can involve repeated or constant breathing difficulty, fluid in the lungs, weakness, fainting, poor appetite, fluid in the belly, trouble resting comfortably, and less interest in normal activities. Your dog may not show pain the way a person does, but severe breathing difficulty, weakness, distress, and being unable to rest are serious suffering.

When you are deciding what comes next, the American Veterinary Medical Association says euthanasia may be appropriate when disease seriously impairs quality of life or needs more care than a family can give. Things to look at together with your vet:

• Breathing comfort, and whether your dog can sleep.
• Appetite and drinking.
• Mobility and interest in family.
• Good days compared with bad days.
• Fainting or emergency episodes.
• Whether the treatment is still giving back comfortable days.

Write down each day as good or bad on a calendar. After a few weeks, the pattern is easier to see, and it gives your vet something concrete to work from. If you are heading into that talk, our when to put a dog down article covers the broader question.

These are short answers to the questions owners ask most.

Coughing, tiring easily, faster breathing at rest or in sleep, fainting, weakness, a swollen belly, and weight loss can all occur. Each one has other possible causes, so a vet needs to look. Go to an emergency vet for breathing hard at rest or blue or gray gums.

There is no single answer. Time depends on the disease, the stage, treatment response, and other illness, and a dog with a murmur but no signs is in a very different place from a dog in advanced heart failure. Ask your vet what the stage and test results mean for your dog.

For mitral valve disease, vets use A, B1, B2, C, and D. A means risk without heart changes, B1 and B2 mean disease without heart failure signs (B2 with clear enlargement), C means current or past heart failure signs, and D means heart failure that has stopped responding to standard treatment.

Often a short, easy walk is fine, but the amount is your vet's decision. Stop if your dog tires, coughs, weakens, or breathes harder, and tell your vet what happened.

Ask your vet, because the answer depends on the stage, the kidneys, and the medicines. Do not start supplements or a big diet change without veterinary guidance, and ask before you offer salty treats or table scraps.

No. A cough can come from the heart, the airways, an infection, or other causes, so it needs a veterinary assessment.

Talk with your vet when breathing trouble keeps coming back, treatment is no longer working, or your dog cannot rest or enjoy normal things. Your vet can help you judge comfort and discuss humane euthanasia when quality of life is seriously impaired.

If your dog is breathing hard at rest, has blue or gray gums, has collapsed, or is severely weak, go to the nearest emergency vet now and stop reading. Our emergency vet directory can help you find one.

If your dog is stable, call your regular vet today. Tell them what you have seen, start counting sleeping breaths, and ask what testing they recommend. I'm not a vet, and I can't diagnose your dog, but you can walk into that visit prepared, with a log, a list of questions, and a clear idea of which signs mean you should not wait.

• American Animal Hospital Association: American Animal Hospital Association
• American Animal Hospital Association: heatstroke in pets
• American Veterinary Medical Association: American Veterinary Medical Association
• cardiacvet.com: Cardiac Vet price list
• hospital.cvm.ncsu.edu: NC State veterinary hospital
• Merck Veterinary Manual: Merck Veterinary Manual
• Merck Veterinary Manual: Merck Veterinary Manual
• Merck Veterinary Manual: Merck Veterinary Manual
• msdvetmanual.com: MSD Veterinary Manual
• onlinelibrary.wiley.com: EPIC study
• PubMed Central: ACVIM consensus guidelines
• spectrumcare.pet: SpectrumCare cost guide
• VCA Animal Hospitals: VCA
• vet.tufts.edu: Tufts Cummings School