Adopting a Cat With a Heart Murmur: 1-6 Grades

A murmur is a sound, not a diagnosis. A grade 2 murmur in a settled 3-year-old cat is often harmless for years, while a grade 4 murmur with a normal-looking cat can sit on top of hypertrophic cardiomyopathy that will need treatment inside 12 months. The 1 to 6 scale is the first filter, grade 3 is the dividing line for echocardiography, and the recheck interval that follows is 6 months for anything above grade 3. Annual cost runs $300 to $900 once the echo is in the plan, and the number is decided by the grade, not by the cat's mood.

The 1 to 6 scale in plain terms

Grade 1 is barely there: audible only in a silent room with the stethoscope pressed hard, easy to miss on a second listen. Grade 2 is soft but unmistakable each time the heart beats. Grade 3 is moderate, about as loud as the normal heart sounds around it. Grade 4 is loud and comes with a thrill, a vibration you can feel through the chest wall with a flat palm. Grade 5 is loud enough to hear with the stethoscope edge lifted off the chest. Grade 6 is audible with the stethoscope fully off the chest, and it is rare.

Grading is subjective. Two vets listening to the same cat on the same day commonly differ by 1 grade, which is why the number is recorded with the date, the vet's name and the cat's position, and why a jump from 2 to 4 over 6 months means more than a single reading of 3.

Why grade 3 is the dividing line

Below grade 3, most vets do no cardiac imaging on the first visit unless there are symptoms, an arrhythmia, or a breed on the list. At grade 3 and above, an echocardiogram is the usual next step, because a loud murmur in a cat is a structural question: thickened wall, dilated atrium, or a normal heart with a fast flow. Above grade 3 the echo stops being optional.

Three exceptions cut across the grades. A kitten under 16 weeks with a soft murmur usually gets a recheck at 5 to 6 months rather than imaging, because many fade as the chest grows. A cat over 8 years with a new murmur gets thyroid and blood pressure checks first, since hyperthyroidism and hypertension both produce one. And any cat, at any grade, that breathes faster than 30 times a minute at rest goes to imaging the same week.

What the 6-month recheck contains

Each visit: auscultation at the same 3 points, resting respiratory rate, weight to 0.1 kg, blood pressure, and an echo every 6 to 12 months depending on what the last one showed. Blood pressure is the cheap test that gets skipped: 2 readings 5 minutes apart, $40 to $80, and a systolic over 160 mmHg changes the plan on its own.

The echo reports 2 numbers worth writing down: the left atrium to aorta ratio, where 1.5 is the usual cut-off for enlargement, and the diastolic wall thickness, where 6.0 mm is the threshold most cardiologists use for hypertrophic cardiomyopathy. A cat at 1.4 and 5.5 mm can wait 12 months; a cat at 1.7 and 6.5 mm is on a 6-month clock and probably on medication.

What each grade costs to follow

Grade	What you hear	First workup	Recheck	Cost (USD)
1	Faint, silent room only	Exam and blood pressure	12 months	80 to 180
2	Soft, clear every beat	Exam, blood pressure, thyroid if over 8 years	12 months	120 to 280
3	Moderate, equal to heart sounds	Echocardiogram	6 to 12 months	300 to 600
4	Loud, palpable thrill	Echocardiogram plus chest film	6 months	450 to 900
5 and 6	Audible off the chest	Echocardiogram, film, blood pressure	3 to 6 months	500 to 1,100

The $300 to $900 yearly figure covers the common middle of that table: 2 exams at $60 to $150 each, 1 echo at $180 to $400, and 2 blood pressure readings at $40 to $80. Year 1 costs more than year 2 because the first echo is usually paired with a film and bloodwork.

Medication is a prescription decision, not an owner one

Drugs for a cat with a murmur, whether a beta-blocker, a diuretic or an anti-clot agent, are started, dosed and stopped only on a veterinary prescription, after an echo and usually after bloodwork. Doses depend on weight, kidney values and the echo findings, and they are not something to adjust at home or copy from another cat. Ask what each drug is for, what side effect would mean stopping, and when the next blood test is due; write all 3 on the discharge sheet.

What to watch between visits

Resting respiratory rate twice a week, counted over 30 seconds while the cat sleeps, is the single best home signal: under 30 is the target, 30 to 35 means a call, above 35 means the same-day visit. Weight loss of 200 g in a month, a new cough, or hiding in a new place are the other 3. Sudden hind limb paralysis, with a cold paw and a crying cat, is a clot and needs the emergency room within 6 hours, because the window for treatment closes fast.

Adopting with eyes open

Ask the shelter for the murmur grade and the date it was heard, in writing. If the grade is 3 or higher and no echo exists, price the echo before signing: $180 to $400 is the number that decides whether the adoption is affordable. The foster-to-adopt route is often the better fit for a grade 4 cat, because 4 to 8 weeks in the foster home shows the respiratory rate, the appetite and the activity level that a 20-minute shelter visit cannot. Keep the first echo report in the same folder as the window and screen notes, and check the yearly total against the cost calculator before the contract is signed.

5 steps in the first month

Get the grade and the date in writing, and have it re-checked by your own vet within 14 days.
Book the echo if the grade is 3 or higher, or if the resting rate is above 30.
Start a 30-second resting rate log, twice a week, same time of day.
Ask for the 2 echo numbers, atrium to aorta ratio and wall thickness, and keep the printout.
Set the 6-month recheck in the calendar on the day of the first visit.

Terms mentioned in this article

Frequently asked

Is a grade 2 murmur in a young cat a reason not to adopt?

Usually not. Grade 2 is soft and clear on every beat, and a large share of young cats with a soft murmur have a normal heart on echo. What matters is the plan: one exam with blood pressure at $80 to $180, a 12-month recheck, and an echo the moment the resting rate passes 30 or the grade rises. A grade 2 cat that stays grade 2 for 2 years is a normal cat with a sound.

Why does a grade 4 murmur need an echo when the cat looks fine?

Because loudness tracks structure, not symptoms. Cats compensate for a thickened heart wall by staying still, and many show no sign until the left atrium enlarges and fluid appears. An echo at $180 to $400 measures the atrium to aorta ratio and the wall thickness, and those 2 numbers decide whether the cat starts medication at the next visit or waits 12 months. Waiting for symptoms usually costs more.

How often should the recheck happen after a grade 5 diagnosis?

Every 3 to 6 months, not yearly. At grade 5 to 6 the usual schedule is an echo every 6 months, blood pressure and bloodwork at each visit, and a resting rate log at home twice a week. Owners who log the rate catch decompensation 1 to 3 weeks before a crisis, which is the difference between a $180 recheck and a $900 emergency stay.