Six numbers carry most of an echo report: LA/Ao ratio, fractional shortening, left ventricular internal diameter in diastole, septal and free wall thickness, and the left atrial size in centimeters. Read them in 3 grades — normal, borderline, abnormal — and the report stops being a wall of jargon.
The 1 number owners remember is LA/Ao at or under 1.5. That single ratio answers whether the atrium is backing up, and it is the number that decides how often the cat comes back.
The 6 numbers, in the order they matter
LA/Ao compares the left atrium to the aortic root on a right parasternal short-axis view. Fractional shortening (FS%) measures how much the ventricle squeezes. LVIDd is the chamber size in diastole. IVSd and LVPWd are the septum and free wall. Left atrial diameter in centimeters gives the absolute size. Everything else on the page supports those 6.
Each number is an average of 3 consecutive beats, measured at end-expiration, on a cat that is not struggling. A single beat taken during a wriggle can read 5 percent off, which is the difference between 1.4 and 1.55.
LA/Ao: the 1.5 line
Under 1.5 is normal. From 1.5 to 1.7 is the equivocal band: the atrium is at the upper limit, and 1 measurement on 1 day is not enough to call it enlarged. Over 1.7 is enlarged, and the same cat's absolute left atrial diameter usually reads above 1.5 cm at that point.
Why the ratio and not just the size: cats come in 2.5 kg and 7 kg bodies, and the aorta scales with the body. LA/Ao removes most of that. It does not remove operator difference — 2 experienced sonographers on the same cat can disagree by 0.1 to 0.2, which is why serial reports from 1 clinic compare better than 2 reports from 2 clinics.
FS%: the 30 to 45 band
Fractional shortening between 30 and 45 percent is the usual normal band on a feline exam. Above 45 percent is hyperdynamic: dehydration, hyperthyroidism, or a cat that is terrified all push it up. From 25 to 30 percent is mildly reduced; under 25 percent is reduced systolic function and is the number that changes a treatment plan.
FS% is load-dependent. A dehydrated cat can read 50 percent with a failing heart, and a cat in fluid overload can read 22 percent with a normal one. That is why the report is read as a set, with LA/Ao and wall thickness, not as 6 independent scores.
Wall thickness: 6 mm is the line
IVSd and LVPWd under 5.5 mm are normal in most cats. From 6.0 to 7.9 mm is hypertrophy, mild to moderate. At 8.0 mm and above it is severe. The 5.5 to 6.0 mm gap is the gray zone where body weight, breed and blood pressure decide the call, and where a repeat in 3 to 6 months is more useful than a label today.
Hypertrophy with a normal LA/Ao and a normal FS% is a different cat from hypertrophy with LA/Ao at 1.9 and FS% at 20. The first may be stable for years; the second is the one that needs the plan.
The 3 grades, plainly
Grade 1, normal: LA/Ao under 1.5, FS% 30 to 45, walls under 5.5 mm, no murmur or a grade 1 soft one. Grade 2, borderline: 1 value sits in a gray band, typically LA/Ao 1.5 to 1.7 or walls 5.5 to 6.0 mm, with everything else normal. Grade 3, abnormal: LA/Ao over 1.7, or FS% under 25, or walls at 6 mm and above with 1 more abnormal value.
The grade is not a diagnosis. It is a summary of how far the numbers sit from the normal band, and it sets the recheck interval: grade 1 in a young cat, 12 months; grade 2, 3 to 6 months; grade 3, 1 to 3 months or sooner if the breathing rate changes.
The 6 rows, with bands
| Parameter | Normal | Borderline | Abnormal |
|---|---|---|---|
| LA/Ao | under 1.5 | 1.5 to 1.7 | over 1.7 |
| FS% | 30 to 45 | 25 to 30 | under 25 or over 45 |
| IVSd, LVPWd | under 5.5 mm | 5.5 to 6.0 mm | 6.0 mm and above |
| LVIDd | 1.2 to 1.8 cm | 1.8 to 2.0 cm | over 2.0 cm |
| Left atrium, absolute | under 1.5 cm | 1.5 to 1.7 cm | over 1.7 cm |
| Aortic root | 0.8 to 1.2 cm | 1.2 to 1.3 cm | over 1.3 cm |
Six rows, 18 numbers. A report that gives 1 ratio and no absolute atrial size is telling you half of what you paid for; ask for both.
What the report cannot tell you
Blood pressure, thyroid level, and hydration all move these numbers without appearing anywhere on the page. A cat with a systolic pressure over 160 mmHg and 6.2 mm walls may have hypertensive remodeling, not primary heart muscle disease. A T4 above 4.0 µg/dL raises FS% on its own. That is why an echo is read with a blood pressure, a chemistry panel and a T4, and why 1 abnormal number in a well cat is a reason for a recheck, not a life sentence.
When to go now, not in 3 months
Resting breathing over 30 breaths per minute at home, an open-mouth breath at rest, hind legs that drag or feel cold (a saddle thrombus), fainting, or a heart rate over 220 at rest. Those are the signs that turn a scheduled echo into an emergency visit, and they outrank any ratio on a report from last month.
5 steps to read a report in 10 minutes
- Find the reference range printed on the report; labs differ, and a normal for 1 machine is not a normal for another.
- Check LA/Ao first, then the absolute left atrial size in centimeters.
- Compare FS% with hydration and thyroid status before you call it reduced.
- Read IVSd and LVPWd together; 1 wall thickened and 1 normal is a measurement question, not a disease.
- Write the 3 numbers and the date on the fridge, so the next report has something to be compared with.
A murmur workup usually starts with a blood count, and the ranges plus the stress response are set out in the WBC guide; breeds with a known tendency to thick heart muscle are listed in the breed quiz.
Terms mentioned in this article
Frequently asked
LA/Ao is 1.6. Does the cat have heart disease?
Not necessarily. From 1.5 to 1.7 is the equivocal band, and 1 measurement on 1 day is not enough. Ask for the absolute left atrial size in centimeters, the wall thickness, and a repeat in 3 to 6 months. A single ratio in a cat with no murmur and no clinical signs is a reason to recheck, not to treat.
Why does FS% differ between 2 reports on the same cat?
Fractional shortening depends on hydration, blood pressure, sedation and fear, and it also depends on where the operator places the calipers. A 5 to 10 point swing between 2 visits is common when the cat was dehydrated at 1 visit and well hydrated at the other. Compare LA/Ao and wall thickness as well.
How often should a cat with a heart murmur be scanned?
It follows the grade on the report: 12 months for a normal study, 3 to 6 months for 1 borderline value, and 1 to 3 months for an enlarged atrium or reduced function. Any change in resting breathing rate, appetite or hind leg strength moves the next scan sooner, whatever the schedule says.