A murmur heard through a stethoscope is a screening result, not a diagnosis. In cats, the number that changes what happens next is grade 3: grades 1-2 in a quiet, calm cat usually mean a recheck in 6-12 months, while grade 3 and above means an echocardiogram before anything else is decided. The second number is the resting breathing rate, counted over 30 seconds and doubled, with 30 breaths per minute as the line where a routine visit becomes a same-week appointment.
Both numbers are cheap to obtain. One takes a stethoscope in a quiet room; the other takes a phone timer and a sleeping cat. Together they decide more than any single blood test, and neither requires the cat to be sedated.
What the 1-6 scale actually measures
Loudness, and nothing else. Grade 1 is audible only in a silent room with a still cat; grade 2 is soft but present the moment the chest piece lands; grade 3 is as loud as the normal heart sounds; grade 4 is louder than the heart sounds but still needs full contact; grade 5 is audible with only the edge of the diaphragm touching; grade 6 is audible with the stethoscope lifted off the chest wall. The scale describes turbulence and transmission, not the severity of the disease behind it.
That gap matters in both directions. A grade 2 murmur in a cat with severe septal thickening can be more dangerous than a grade 4 murmur generated by high flow in a thin, febrile or anemic cat, where the heart itself is normal. Roughly 3 in 10 cats with hypertrophic cardiomyopathy (HCM) have no murmur at all on the day of examination, so a quiet chest never rules the disease out. The grade tells you how loudly blood is complaining, not how sick the muscle is.
Why grade 3 is the echo line
Below grade 3, a young cat with a soft murmur and a normal exam can reasonably be watched, because innocent flow murmurs are common and most do not progress. At grade 3 and above, the pretest probability of structural disease is high enough that an echo changes management, and the echo is the only test that measures wall thickness, chamber size and dynamic obstruction directly. Ask for measured values, not adjectives: interventricular septum and free wall thickness in diastole, with 6 mm as the usual upper limit for a normal cat, left atrial to aortic root ratio with 1.5 as the upper limit, and a note on systolic anterior motion of the mitral valve. The whole cascade is laid out in the HCM screening page, and one echo runs 400-900 RMB by clinic (cost tables).
Grade is also position dependent. A murmur heard at the left apex may be inaudible at the right sternal border, and a cat that is purring, shivering or breathing loudly can hide a grade 2 entirely. If the cat will not settle, ask for a second auscultation on a different day rather than accepting a single normal report.
Screening intervals by age and grade
| Age | Grade | Test | Recheck interval |
|---|---|---|---|
| Under 6 years | 1-2, no signs | Auscultation plus resting breathing log | 12 months |
| 6-10 years | 1-2, no signs | Baseline echo, blood pressure | 12-18 months |
| Any age | 3 or higher | Echo plus blood pressure | 6 months, or as directed |
| Any age | 4-6 or gallop rhythm | Echo, chest x-ray, NT-proBNP | 3 months |
| Any age | Any grade, breathing over 30 | Echo within 7 days | As directed |
Breed matters inside those intervals. A Maine Coon or Ragdoll with any murmur gets an echo earlier, because both breeds carry a familial form of HCM and a first-degree relative with the disease raises the prior. A domestic shorthair at 12 years with a grade 1 murmur and a breathing rate of 18 needs a log and a recheck, not a cardiology referral in the same week.
The 30-breath rule, measured properly
Count chest wall movements while the cat is asleep and unaware, for 30 seconds, then multiply by 2. One rise and fall is one breath. Do it at the same time each day, ideally in the morning before feeding, and write it down, because a single number means little and 7 days of numbers means a trend. A sleeping cat normally sits between 16 and 30 breaths per minute; 30 is the alarm line, not the average. Ranges for temperature, pulse and gum colour are in the vital signs table.
Escalate in steps. A rate of 30-40 that persists over 2 consecutive days earns a call and an appointment within 48 hours. A rate above 40 at rest, open-mouth breathing, or a cat that will not lie down is an emergency tonight, because those three together point to fluid in or around the lungs rather than to a stable murmur. A rise from a personal baseline of 18 to 26 over one week matters even though 26 is inside the normal range.
Before anesthesia, and before breeding
Any cat with a murmur needs an echo before a dental or any procedure requiring general anesthesia, and the echo should be no more than 3-6 months old on the day of the procedure, since wall thickness and obstruction can shift in that window. Breeding cats need an echo before the first mating, and a cat with documented HCM should not be bred at all. The same echo answers the anesthetic question and the genetic one, which is why it is worth doing once, properly, rather than repeating a cheaper test.
What to do with a grade 1 murmur at 12 years
Most of the management is a log and a calendar, not a drug. Record the breathing rate daily for 7 days, weigh the cat monthly, and book the echo within 3 months if it has never been done. Ask about appetite and activity at each visit, because a cat that stops jumping onto the bed is often showing you cardiac or joint disease 3-6 months before either is obvious on examination. Medication is started on the basis of measured disease and clinical signs, and most cardiologists will not start it for a murmur alone.
Five things to do this week
- Count resting breathing for 30 seconds tonight, then daily for 7 days, and keep the numbers in one place.
- Ask for the grade in numbers at the next visit, plus the location, and write both into the record.
- Book an echo if the grade is 3 or higher, or if the cat is a Maine Coon or Ragdoll with any murmur.
- Weigh the cat monthly; a 5 percent drop in 8 weeks is a reason to move the echo forward.
- Put the emergency number and the 40-breath rule on the fridge, where someone else can find them.
Terms mentioned in this article
Frequently asked
Does a grade 2 murmur mean my cat has heart disease?
Not necessarily. Grade describes loudness only, and soft murmurs are common in young cats and in cats that are thin, anemic or febrile. What matters is the echo: wall thickness under 6 mm, a left atrial to aortic ratio under 1.5 and no obstruction all point to a benign finding. Ask for the measured numbers rather than accepting a description of the sound.
How often should a cat with HCM be rechecked?
Most cardiologists recheck an echo every 6 to 12 months for a stable cat, and every 3 to 6 months once there are signs such as a rising breathing rate. Between visits, count the resting breathing rate daily for 30 seconds and keep the log, because a rise from 18 to 26 over a week can move the appointment forward before any other sign appears.
When is fast breathing an emergency?
A sleeping rate above 40 breaths per minute, open-mouth breathing, and a cat that will not lie down are emergency signs and should be seen tonight, since they can indicate fluid around the lungs. A rate of 30 to 40 that persists for 2 days earns a call and a visit within 48 hours rather than a wait for the next scheduled recheck.