A "saddle thrombus" in cats is sudden hind-limb paralysis caused by a blood clot that lodges where the aorta splits to supply the back legs. It is one of the most painful emergencies in feline medicine: cats present with cold paws, crying, dragging one or both back legs, and rapid breathing. Most are caused by underlying hypertrophic cardiomyopathy. This is always an ER, not a wait-and-see — and many cats are humanely euthanized at presentation because of severe pain and a poor long-term prognosis.
Last reviewed: May 2026
What Is a Saddle Thrombus in Cats?
A saddle thrombus is the common name for feline aortic thromboembolism (ATE) — a clot that forms in the enlarged left atrium of the heart, breaks loose, and lodges at the terminal bifurcation of the aorta where it divides into the right and left iliac arteries. The clot blocks blood flow to the back legs, causing acute paralysis, severe pain, cold limbs, and absent pulses. About 90 percent of feline ATE cases are caused by underlying cardiomyopathy — most often hypertrophic cardiomyopathy, but also restrictive and unclassified forms.
The "saddle" name comes from the way a single clot straddles the aortic bifurcation like a saddle on a horse. Cats can also throw smaller clots to one back leg, a front leg, the brain, or the kidneys, with proportionally smaller but still serious deficits.
Symptoms — The Classic "Five P's"
The classic presentation involves five P's: paralysis, pain, pallor, pulselessness, and poikilothermia (cold legs). A cat with a saddle thrombus typically vocalizes loudly, drags both back legs, has cold pale or blue-tinged paw pads, has no detectable femoral pulse, and is breathing rapidly because of concurrent congestive heart failure. Onset is dramatic and almost always within minutes; owners often describe it as a sudden scream followed by collapse.
About 70 to 80 percent of cats have no prior cardiac diagnosis at the time of the saddle thrombus — the clot is the first warning the owner ever sees, as described in Nelson and Couto's Small Animal Internal Medicine. Concurrent congestive heart failure is present in roughly half of cases.
Why It Hurts So Much
The pain of acute ischemia is among the most severe encountered in any species. The blocked blood supply causes nerve and muscle ischemia, and within minutes a chemical "reperfusion injury" cascade also develops. Aggressive pain control — typically intravenous opioids and sometimes additional sedation — is the first priority once a saddle thrombus is suspected. Pain control improves outcome and is humane regardless of long-term plan.
Diagnosis
A confident diagnosis is usually made on exam — cold paws, paralysis, absent pulses, often with detectable heart murmur or gallop sound. Doppler blood pressure measurement at the back leg shows no flow. Bloodwork commonly shows markedly elevated AST and CK from muscle ischemia, and elevated potassium during reperfusion. An echocardiogram performed once the cat is stabilized confirms underlying cardiomyopathy and atrial enlargement. NT-proBNP is usually elevated, supporting the cardiac origin.
Treatment and Prognosis
Treatment is aggressive pain control (opioids), thromboprophylaxis with clopidogrel and sometimes low-molecular-weight heparin, supportive care, and management of any concurrent congestive heart failure. Thrombolytic drugs (tissue plasminogen activator) have been studied but carry high bleeding risk and have not shown clear survival benefit. Most cats are managed medically with intensive supportive care.
Reported overall survival to hospital discharge is approximately 30 to 45 percent. Of cats that survive the acute event, most regain some limb function within 1 to 6 weeks, though many have residual deficits. Median post-discharge survival is roughly 4 to 6 months because of progression of the underlying heart disease and risk of repeat clot events. The standard cardiology framework guides triage and prognostication (Luis Fuentes et al., 2020, JVIM (ACVIM Consensus on Feline Cardiomyopathies)).
Can a Saddle Thrombus Be Prevented?
Cats with known cardiomyopathy and an enlarged left atrium are at high risk. Clopidogrel (an anti-platelet drug given daily by mouth) reduces the risk of a first or recurrent ATE event by about 60 percent compared with aspirin in cats with prior ATE, and is the current standard of care for at-risk cats. Identifying cardiomyopathy before it causes a clot — through routine senior wellness exams, careful auscultation, and screening NT-proBNP or echocardiogram in at-risk breeds — is the most powerful preventive step, in line with current feline preventive care recommendations (AAFP-AAHA Feline Life Stage Guidelines, 2021).
When to See a Vet
A saddle thrombus is an emergency at presentation — there is no version of this that is wait-and-see. The lists below help you separate the warning signs of underlying cardiac disease (call-today) from the acute event (ER now).
Call your vet today if:
- New heart murmur found on an exam, especially in a Maine Coon, Ragdoll, or Sphynx
- Sleeping respiratory rate consistently above 30 breaths per minute
- Cat tires easily, hides more, or has lost weight subtly over months
- Cat is on cardiac medication and you have missed any doses
- Cat has known HCM with an enlarged left atrium and is not on clopidogrel
Go to the ER immediately if:
- Sudden paralysis or dragging of one or both back legs
- Crying out, screaming, or obvious severe pain
- Cold, pale, or blue paw pads on the back feet
- Inability to stand combined with rapid or open-mouth breathing
- Collapse or weakness with any of the above signs
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Frequently Asked Questions
Can a cat recover from a saddle thrombus?
Approximately 30 to 45 percent of cats survive to hospital discharge after a saddle thrombus, and of those, most regain partial to full back-leg function over 1 to 6 weeks. However, median survival after discharge is only about 4 to 6 months because of the underlying heart disease and a substantial risk of repeat clot events. Many owners elect humane euthanasia at presentation given the pain and poor long-term outlook — this is a reasonable, kind decision.
How much does saddle thrombus treatment cost?
Initial ER evaluation and pain control runs $400 to $1,000, and hospitalized care for 2 to 5 days typically costs $2,000 to $5,000 depending on intensity. Long-term cardiac medication (clopidogrel, heart failure drugs, rechecks) is $50 to $200 per month. Owners should be aware that even with full intensive treatment, prognosis is guarded — the cost-of-care conversation is part of every ER triage.
Is saddle thrombus very painful?
Yes — ischemic limb pain from acute arterial blockage is among the most severe pain encountered in any species. This is why prompt opioid pain control is the first medical priority, and why many owners and vets discuss humane euthanasia compassionately at presentation. Continuing without strong pain control is not humane.
Could this have been prevented?
In some cases, yes. Cats with known cardiomyopathy and enlarged left atria benefit from daily clopidogrel, which reduces the risk of first or recurrent thrombus events by about 60 percent. Annual physical exams that catch new heart murmurs, and screening NT-proBNP or echocardiogram in at-risk breeds (Maine Coon, Ragdoll, Sphynx, British Shorthair), can identify the underlying cardiomyopathy before a thrombus event.
Why are the back legs cold?
The clot at the aortic bifurcation cuts off arterial blood flow to both back legs. Without blood flow, the tissue cools rapidly to room temperature and the paw pads lose color (pallor or cyanosis). This is one of the most reliable physical exam findings and is part of how vets confirm the diagnosis without waiting for imaging.
Still Not Sure if Your Cat Needs a Vet?
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