Heart Murmur in Dogs: What It Means, Signs to Watch For, and When to Act
"Your dog has a heart murmur" — three words that can make any pet owner's heart sink. But a murmur diagnosis doesn't automatically mean your dog is in immediate danger. Understanding what a murmur actually is, what grade it is, and what symptoms to watch for at home can make the difference between appropriate monitoring and a missed emergency. In 2026, heart murmurs are one of the most commonly detected findings at routine vet checkups for middle-aged and senior dogs.
What Is a Heart Murmur?
A heart murmur is an abnormal sound heard through a stethoscope during the heartbeat cycle — a whooshing, swishing, or rumbling sound caused by turbulent blood flow through or near the heart. Normal heart sounds are two clean beats: "lub-dub." A murmur appears as an extra sound within that rhythm.
According to VCA Animal Hospitals, murmurs are graded on a scale of 1 to 6 based on loudness:
| Grade | Description |
|---|---|
| 1 | Very faint; heard only in ideal conditions |
| 2 | Soft but consistently heard |
| 3 | Moderate; heard easily |
| 4 | Loud; heard with stethoscope placed anywhere on the chest |
| 5 | Very loud; stethoscope barely needs to touch the chest |
| 6 | Heard without a stethoscope (extremely rare) |
Grade 1–2 murmurs are often "innocent" — particularly in puppies and young adult dogs — and may never cause problems. Grade 3–6 murmurs are more likely to indicate significant heart disease.
What Causes Heart Murmurs in Dogs?
Structural Heart Disease
The most common cause in dogs is degenerative mitral valve disease (DMVD) — a thickening and leaking of the mitral valve that separates the left atrium and ventricle. DMVD is extremely common in small breeds, particularly:
- Cavalier King Charles Spaniels (nearly universal by age 10)
- Dachshunds
- Miniature and Toy Poodles
- Chihuahuas
- Shih Tzus
Large breeds, particularly Doberman Pinschers and Great Danes, are prone to a different condition: dilated cardiomyopathy (DCM), which can also cause murmurs.
Innocent/Physiologic Murmurs
Found in puppies (usually grades 1–3), these resolve on their own as the heart matures — typically by 4–6 months of age. They are not caused by structural heart disease.
Other Causes
Anemia, infections, high blood pressure, and extracardiac conditions can all cause functional murmurs without underlying structural disease.
Symptoms Associated With Heart Murmurs
A Grade 1–2 murmur in an otherwise healthy dog may cause no symptoms at all. As disease progresses, symptoms of congestive heart failure (CHF) can develop:
- Coughing — particularly at rest or at night, or a new cough that develops in a dog with a known murmur
- Rapid breathing rate at rest — Cornell University notes that a resting respiratory rate above 30 breaths per minute in a dog warrants prompt evaluation
- Exercise intolerance — tiring on walks that used to be routine
- Lethargy — general fatigue and disinterest in activity
- Abdominal distension — fluid accumulation in the belly (ascites)
- Fainting or collapse — arrhythmias caused by heart disease
- Pale or bluish gums — indicating poor oxygenation
The 30 Breaths Per Minute Rule
Cornell University's Riney Canine Health Center emphasizes this critical monitoring tool for dogs with known heart disease: count your dog's resting respiratory rate (RRR) once daily. Count breaths for 30 seconds while your dog is sleeping, then multiply by two.
- Normal: Under 30 breaths/minute
- Concerning: 30–35 breaths/minute — call your vet
- Emergency: Above 35 breaths/minute — go to the vet now
This simple, free daily measurement can help you catch early heart failure before your dog shows other obvious symptoms.
When to Worry: Emergency Signs
Go to an emergency vet immediately if your dog has:
- Labored breathing at rest, with abdominal effort to breathe
- Blue or purple gums or tongue
- Sudden collapse or fainting
- A resting respiratory rate above 35 breaths per minute
- Coughing that won't stop for more than a few minutes
If you've noticed your dog is losing balance or seems extremely fatigued alongside a known murmur, go to the vet the same day.
How Voyage Can Help
If your dog has been diagnosed with a heart murmur and you're monitoring their breathing rate at home, Voyage AI Vet can help you assess whether the numbers and symptoms you're seeing indicate it's time to go in. Starting at $4.99/month, it's the quickest way to get guidance at 11 PM when your dog's breathing seems faster than usual.
Frequently Asked Questions
Q: My dog was just diagnosed with a heart murmur — how long do they have? A: This depends entirely on the grade, underlying cause, age, and breed. Many dogs with low-grade murmurs live years without developing heart failure. Cavalier King Charles Spaniels may progress faster than other breeds. Your vet will recommend echocardiography and follow-up based on grade and breed.
Q: Should a dog with a heart murmur still exercise? A: Mild to moderate exercise is generally fine for dogs with low-grade murmurs and no heart failure. Dogs in active heart failure need exercise restriction. Ask your vet for specific guidance based on your dog's cardiac status.
Q: Can a heart murmur go away on its own? A: Innocent puppyhood murmurs often do resolve. Adult-onset structural murmurs (like DMVD) do not reverse — they may progress at varying rates.
Q: When does a heart murmur need medication? A: Medication (typically pimobendan) is now recommended for dogs with evidence of cardiac enlargement on chest X-ray or echocardiogram before they reach heart failure — this has been shown to delay the onset of CHF significantly.
This article is for informational purposes only and is not a substitute for professional veterinary advice. Please consult a licensed veterinarian for any health concerns about your dog.