Overview

RCM impairs left ventricular relaxation during diastole. Unlike HCM, wall thickening is not its defining feature. Stiff myocardium or fibrosis of the endocardium and inner layers prevents normal expansion. Poor ventricular filling leads to blood backing up into the left atrium, progressive atrial enlargement and increased pulmonary venous pressure.

RCM often progresses quietly. The left atrium may be markedly enlarged before an owner notices a change. Enlargement promotes blood stasis and clot formation. A detached clot lodging at the aortic branch to the hindlimbs can cause sudden hindlimb paralysis (ATE).

Cats more often affected

RCM can affect any breed, but is reported more often in cats with these characteristics:

Middle-aged or older, with detection becoming more frequent from about age 8
Left atrial enlargement found at a previous screening
A murmur or gallop sound detected on auscultation
Impaired relaxation during follow-up of another cardiomyopathy such as HCM
Age-related concurrent disease such as hyperthyroidism or chronic kidney disease

Some cats have no audible murmur even at screening. Subtle breathing and activity changes are also useful clues.

What signs should I watch for?

Cats often hide discomfort, making early RCM difficult to recognize. Repeated occurrence of two or more of these signs warrants imaging assessment.

Repeated increases above the usual sleeping respiratory rate
Open-mouth, panting-like breathing — very unusual in cats
Reduced activity or avoidance of play and jumping
Reduced appetite, weight loss or less grooming
Sudden hindlimb paralysis or pain — possible ATE requiring immediate care at the nearest 24-hour emergency veterinary hospital
Fainting or loss of consciousness — possible concurrent arrhythmia

Left atrial enlargement is a key RCM finding

The central changes are left atrial enlargement and impaired relaxation, not left ventricular wall thickness. Marked atrial enlargement warrants assessment of ATE risk alongside pulmonary edema and pleural effusion. Antithrombotic care may be considered even before symptoms.

Diagnostic steps

RCM diagnosis combines information gathered in stages rather than one test alone.

Auscultation

Assess murmurs, gallops and arrhythmias. Cats may have RCM without a murmur, so normal auscultation does not end the assessment.
Chest X-rays

Assess the cardiac silhouette, changes suggesting left atrial enlargement, pulmonary venous congestion, edema and pleural effusion. Cats with breathing difficulty are assessed promptly with minimal restraint.
Echocardiography

Measure atrial and ventricular size, wall thickness and diastolic indices (E/A and E/E′), and assess spontaneous echo contrast (SEC), indicating blood stasis. Echocardiography is central to RCM diagnosis and differentiation from HCM.
Blood tests + NT-proBNP

Assess kidney function, thyroid hormone (T4), electrolytes and NT-proBNP. NT-proBNP can be useful as a supporting marker of occult feline cardiomyopathy.
Blood pressure / ECG

Measure noninvasive blood pressure for hypertension and add ECG if arrhythmia is suspected. Consider the effects of concurrent hyperthyroidism or kidney disease.

Stages of progression

The ACVIM consensus classifies feline cardiomyopathy into asymptomatic, symptomatic and advanced stages. RCM management follows this framework.

Stage	Condition	When to consider treatment
A	Risk factors for cardiomyopathy but no imaging evidence	No medication needed; regular auscultation and examinations recommended
B1	Mild imaging abnormalities without clear left atrial enlargement	Medication is usually unnecessary; imaging follow-up every 6–12 months
B2	Clear left atrial enlargement without symptoms	Consider antithrombotic medication according to clotting risk
C	Current or previous heart failure signs, including pulmonary edema or pleural effusion	Combination treatment including diuretics and clot prevention
D	Refractory heart failure with reduced response to standard treatment	Dose adjustments, additional medications and intensive monitoring

This owner-oriented table summarizes general ACVIM consensus guidance. Application depends on the individual patient and veterinarian's assessment.

Treatment and care by stage

RCM care aims to reduce left atrial load, prevent clot formation and identify pulmonary edema early. We consider stage and concurrent conditions in the following approach.

Medication combinations by stage

Marked atrial enlargement may warrant antithrombotic medication. Pulmonary edema or pleural effusion calls for combinations centered on diuretics. Antiarrhythmics may be added for rhythm disturbances. Kidney function, electrolytes and blood pressure guide dose adjustments.

Home monitoring — Resting respiratory rate (SRR)

Count breaths for one minute while your pet sleeps and compare with the usual rate. Contact the veterinarian if faster breathing recurs and agree on individual contact thresholds. For labored or open-mouth breathing, go straight to the nearest 24-hour emergency veterinary hospital regardless of the count.

Diet and daily care

Reducing stress is part of treatment: familiar resting spaces, gentle handling and avoiding unnecessary travel or conflict between cats. Sodium restriction depends on stage. Consistent medication times help reduce variation in effect.

Complications and referral

We provide daytime hospitalization only. Patients needing 24-hour hospitalization, intensive care or arrhythmia procedures are referred to cooperating centers. We coordinate imaging, ECG and medication assessment so care remains connected.

Frequently asked questions

How do RCM and HCM differ?

HCM is characterized by thickened left ventricular walls; RCM involves stiffness or endocardial fibrosis impairing relaxation, potentially without wall thickening. Left atrial enlargement signals progression in both. Echocardiography distinguishes them.

Can my cat have RCM without a murmur?

Yes. Cardiomyopathy can occur with little or no murmur. Repeated faster breathing, reduced activity or appetite changes warrant echocardiographic assessment.

Is ATE common in RCM?

ATE risk rises in cats with marked left atrial enlargement. We assess atrial size and blood stasis to consider when antithrombotic medication is appropriate.

Will medication be lifelong?

Medications such as antithrombotics or diuretics introduced at stage B2 or beyond may be needed long term. Choices and doses can change with stage, concurrent disease and kidney function.

How often should my cat be checked?

Older cats should have annual auscultation. If left atrial enlargement has been observed, echocardiographic follow-up every 6–12 months is recommended.

My cat strongly dislikes restraint. Can testing still be done?

Restraint stress can burden the heart, so we divide testing into steps with minimal restraint. If breathing difficulty is suspected, stabilization takes priority before assessment.

References

These external resources explain RCM classification and management in more detail. They do not define our services or an individual prescription.

Restrictive cardiomyopathy (RCM)