Heart Murmur in Dogs: What It Means and What Happens Next

What it usually means

Blood normally flows through the heart smoothly and quietly. When it becomes turbulent, for example because a valve is leaking or narrowed, or there is an abnormal opening between chambers, the vet hears a whoosh between the normal heartbeats. VCA explains that murmurs are graded from 1, very quiet and sometimes only heard on and off, to 6, loud enough to feel through the chest wall. Loudness does not always match how serious the underlying problem is.

The cause depends a lot on age. Innocent, or physiologic, murmurs are common in fast-growing puppies; the AKC cites an estimate of about 28 percent of puppies under six months, and VCA notes they usually appear around 6 to 8 weeks and fade by 4 to 5 months. In older dogs the most common cause is mitral valve disease, a leaky valve that is especially common in small breeds. Other causes include dilated cardiomyopathy in large breeds, inherited defects present from birth, and conditions outside the heart such as anemia, fever, pregnancy or an overactive thyroid.

Signs that the heart is affected

Many dogs with a murmur have no signs at all, especially early on, which is why murmurs are usually found at a routine checkup. VCA notes signs of heart disease may be subtle until it is advanced. Watch for coughing, especially at night or after lying down, tiring quickly on walks, breathing faster or harder than usual at rest or during sleep, restlessness at night, and reduced appetite or weight loss.

More serious signs include fainting or collapse, pale or bluish gums, a swollen belly, and in puppies, poor growth compared with littermates. Counting your dog's breathing rate while it is sleeping, the number of breaths in one minute, is a simple, useful check that your vet may ask you to do at home.

When to call your vet today

Call your vet within a day or two if your dog has a known murmur and starts coughing more, tires on walks, breathes faster at rest, seems restless at night, or eats less. If your vet has given you a target resting breathing rate, call when your dog's sleeping rate stays above it.

Also book a visit if you have a puppy with a murmur that has not faded by about five months, or if your vet heard a murmur and you have not yet had the follow-up tests they suggested. Murmurs found before a planned anesthetic, such as a dental, are worth discussing first.

When it's an emergency

Go to your vet or the nearest emergency vet immediately if your dog is struggling to breathe, breathing very fast with its mouth open while resting, has blue, gray or very pale gums, collapses or faints, or has a swollen, tight belly. These can be signs of heart failure or a dangerous heart rhythm.

Keep your dog calm and cool, avoid making it walk, and call ahead so the team can have oxygen ready. Bring a list of any heart medicines your dog takes and the time of the last dose.

What you can safely do at home

If your vet has found a murmur, keep a simple log of your dog's energy, coughing and sleeping breathing rate, and keep your dog at a healthy weight, which eases the work of the heart. Regular, moderate exercise is usually fine unless your vet advises otherwise, but avoid hard exertion in the heat.

Do not give supplements, human heart medicines or change to a special diet without your vet's advice. Some diets and supplements are not suitable for dogs with certain heart conditions, and the right plan depends on the cause of the murmur.

What the vet will likely check

Your vet will listen carefully to grade and locate the murmur, check pulses, gum color and breathing, and ask about any signs at home. Further tests may include chest X-rays to look at heart size and the lungs, an ECG to check rhythm, blood tests, blood pressure measurement, and a heart-specific blood test.

VCA describes an echocardiogram, an ultrasound of the heart with Doppler, as the most useful test for finding the murmur's source, and many dogs are referred to a veterinary cardiologist for it. Innocent murmurs need only monitoring. Other murmurs are treated according to the cause: some dogs are rechecked periodically, others start medicine at a particular stage of valve disease, and some birth defects can be corrected with surgery.

Prevention and long-term care

Most causes of heart murmurs cannot be prevented, but early detection lets your vet start monitoring or treatment at the right time. Keep up with yearly checkups, and twice a year for older small breeds if your vet suggests it. Good dental care, a lean body condition and regular exercise all support heart health.

If you are getting a puppy from a breed prone to inherited heart disease, ask the breeder about heart screening of the parents. For a dog with a diagnosed murmur, keep rechecks on schedule and learn the warning signs so changes are caught early.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.