A murmur grade describes loudness, not severity, and in cats the two come apart more than in any other species. A cat with hypertrophic cardiomyopathy (HCM) can carry a grade 1 murmur or none at all, while a cat with mild dynamic outflow turbulence can hit grade 3 to 4. The number still matters, because grade 3 is the usual trigger for an echocardiogram and grade 4 and above means a palpable thrill. Read the grade together with 3 things: breathing rate at rest, ability to jump, and appetite.
What the 1 to 6 scale measures
The Levine scale is a loudness scale, graded by how hard the examiner has to work to hear the sound in a quiet room. Grade 1 is the faintest murmur audible only after several seconds of careful listening. Grade 2 is soft but heard immediately when the stethoscope lands. Grade 3 is as loud as the normal heart sounds. Grade 4 is louder than the heart sounds and comes with a thrill, a vibration felt through the chest wall. Grade 5 is very loud with an obvious thrill, and grade 6 is audible with the stethoscope lifted off the chest.
Two examiners can disagree by 1 grade on the same cat, and that is normal. A grade 2 becoming a grade 3 across visits may be the same heart and a different room, so the trend matters more than any single number.
Why grade does not track severity in cats
Murmur loudness depends on turbulence, blood velocity and how much air sits between the heart and the chest wall, not on how thick the heart muscle is. HCM thickens the left ventricle to 6 mm or more in diastole (normal is under 5 mm, 5 to 6 mm is borderline) and often produces little turbulence at rest, so a cat can have severe disease with a grade 1 murmur. Conversely, a young cat with a fast heart rate, mild anemia or a dynamic outflow gradient can produce a grade 3 to 4 murmur with a structurally normal heart.
What the grade does predict is the odds that a cardiologist will find something, which is why it drives the decision to image rather than the decision to treat.
Grade 3 and above: the echo threshold
Above grade 3, or any murmur with a gallop rhythm, arrhythmia or clinical signs, the next step is an echocardiogram: wall thickness in diastole, left atrium to aorta ratio (normal under 1.5, enlarged above 1.7), and systolic function. A grade 1 to 2 murmur in a healthy young cat can reasonably be watched with auscultation every 6 months, but a grade 1 to 2 murmur in a cat over 8 years old still deserves blood pressure and a T4, as the senior murmur workup sets out, because hyperthyroidism and hypertension both create murmurs that resolve when the underlying problem is treated.
| Grade | What is heard | Thrill | Weeks to echo | Recheck (months) |
|---|---|---|---|---|
| 1 | Faintest, only in a silent room | No | 8 to 12 | 6 |
| 2 | Soft, heard on first contact | No | 4 to 8 | 6 |
| 3 | As loud as the heart sounds | No | 2 to 4 | 3 to 6 |
| 4 | Louder than the heart sounds | Yes | 1 to 2 | 3 |
| 5 | Very loud, thrill easy to feel | Yes | 1 | 1 to 3 |
| 6 | Audible off the chest | Yes | 0 | 1 |
Zero weeks means the same day. The table is a starting point, not a protocol. A grade 2 murmur with a resting breathing rate of 34 breaths per minute outranks a grade 4 murmur in a cat that climbs stairs without pausing.
The 6-month recheck
Six months is the standard interval for a stable cat, and the visit is cheap if it is done properly: auscultation in a quiet room, blood pressure by Doppler or oscillometric cuff, body weight, and 3 questions about breathing rate in sleep, jumping height and appetite. An echocardiogram is repeated every 6 to 12 months, or sooner if the murmur rises by 2 grades, the left atrium ratio crosses 1.7, or the cat starts coughing.
Bring a 7-day log of sleeping respiratory rate. Counting breaths for 30 seconds while the cat sleeps and writing down the number, twice a day, is the single most useful home measurement in feline cardiology, and it costs nothing.
Three signs that override the grade
1. Breathing. A sleeping rate under 30 breaths per minute is normal; 30 to 40 sustained over 2 days means a visit within 24 to 48 hours; above 40, or any open-mouth breathing, is an emergency today. 2. Legs. A cat that suddenly drags a hind leg, cries when lifted and has cold paw pads has an aortic thromboembolism, and the first 6 hours matter most. 3. Body. Losing 5 percent of body weight in 3 months, or eating less for a week, moves a stable murmur into a workup, because heart failure and hyperthyroidism both start this way.
Cats hide all 3 well. A cat that stops jumping onto the bed, sleeps more and eats slightly less has usually been compensating for weeks.
What else makes a murmur
Anemia with a hematocrit under 20 percent, fever, a fast heart rate over 220 beats per minute, hyperthyroidism with a T4 above 4.0 micrograms per deciliter, and systolic blood pressure above 160 mmHg can all produce a murmur in a structurally normal heart. That is why the first workup of a new murmur in a cat over 8 years includes a T4, a blood pressure and a renal panel, not just an echo.
When to go now
Same day for open-mouth breathing, a resting rate above 40, blue or grey gums, or sudden hind-limb paralysis. Within 24 to 48 hours for a new cough, a rate of 30 to 40 that persists, or fainting. Within 1 week for a murmur that jumped 2 grades, a new gallop sound, or weight loss the owner can see at the spine and hips.
Five things to do this week
- Count sleeping breaths twice a day for a week and write the numbers down.
- Ask for the grade in writing at the next visit, plus whether a thrill was felt.
- Book blood pressure and a T4 before the echo if the cat is over 8 years old.
- Photograph the cat from above monthly, so 5 percent weight loss is visible early.
- Keep all medications, including any human drug, away from the cat and check every plant against a toxicity list.
The grade is a door, not a diagnosis: it decides whether the cat gets an ultrasound this month or in 6 months. Breathing rate at rest is what tells you whether the heart is failing, and that number is available to any owner with a clock and a sleeping cat.
Terms mentioned in this article
Frequently asked
Is a grade 3 murmur serious in a cat?
Grade 3 is the usual threshold for an echocardiogram, not a verdict. In cats, loudness correlates poorly with disease severity, so a grade 3 murmur can belong to a structurally normal heart with a fast rate, or to cardiomyopathy. The echo measures wall thickness, left atrium size and function, and that is what decides whether treatment or a 6-month recheck is next.
How often should a cat with a heart murmur be rechecked?
Twice a year for a stable cat, with an echocardiogram every 6 to 12 months, plus blood pressure and a T4 in cats over 8 years old. Recheck sooner if the grade rises by 2, the left atrium to aorta ratio passes 1.7, the sleeping breathing rate stays above 30, or the cat starts coughing or losing weight.
Can a murmur go away on its own?
It can when the cause is outside the heart. Anemia, fever, hyperthyroidism and blood pressure above 160 mmHg all produce murmurs that resolve once the underlying problem is treated, which is why a first workup includes a T4, a blood pressure and a blood count. A murmur from cardiomyopathy does not disappear, but it can stay stable for years.