CONDITION
Aortic Thromboembolism in Cats
Aortic thromboembolism describes what happens when a blood clot forms in or travels to the aorta — the body's largest artery — and then blocks one or more of the smaller arteries that branch away from it. In cats, this most often affects the arteries supplying the hind legs. The blockage cuts off blood flow, and the affected limb or limbs lose function suddenly. Owners typically notice that their cat cannot use one or both back legs, often quite abruptly. The affected legs may feel cool or cold to the touch, and the cat may vocalise or breathe rapidly. The presentation can appear after a period of seeming normality, or may emerge in a cat already known to have heart disease. Many cats with this pattern have underlying heart muscle disease that created the environment in which a clot could form. This page explores the signals that may prompt concern, what is happening in the circulation and the heart, how the condition is investigated, and the range of approaches that exist. The goal is to orient understanding, not to direct decisions.
Why this matters now
Aortic thromboembolism tends to occur in middle-aged to older cats, with most cases appearing between five and twelve years of age. The condition shows a strong association with underlying heart muscle disease, particularly hypertrophic cardiomyopathy, though other forms of cardiac disease can also create the conditions for clot formation. Male cats may be affected somewhat more frequently than females, and certain breeds — including Ragdolls, Birmans, and Maine Coons — appear at higher risk, likely reflecting their predisposition to the heart conditions that underlie clot formation.
The presentation is often sudden, with owners noticing loss of limb function over minutes to hours. What appears as an abrupt event typically reflects the final stage of a longer process: the heart disease may have been present for months or years, and the clot itself may have formed gradually before breaking loose or growing large enough to block flow. Some cats may recover partial function in affected limbs over days to weeks if collateral circulation develops, though many do not. The risk of recurrence remains elevated in cats that survive the initial event, particularly if the underlying heart disease continues unchecked.
Signals & patterns
Early signals
Sudden hind limb weakness
The cat may begin dragging one or both back legs, or may be unable to stand on them at all. This loss of function can appear over a very short window, sometimes while the owner is in the same room.
Cool or cold paw pads
The affected leg or legs may feel noticeably cooler than the front legs when touched, reflecting the loss of warm blood flow to the tissues. The difference can be subtle or quite pronounced.
Vocalisation or restlessness
Cats may cry out, pant, or appear distressed, often due to pain in the affected limb. The vocalisation may be persistent or come in waves, and the cat may struggle to settle.
Pale or bluish paw pads
The pads of the affected paw may lose their normal pink colour and appear pale, white, or have a greyish-blue tinge. This change reflects the absence of oxygenated blood reaching the tissues.
Absent pulse in affected leg
If an owner is familiar with checking a pulse, they may notice that the femoral pulse in the affected hind leg cannot be felt, while the pulse in an unaffected leg or the front legs remains present.
Later signals
Muscle stiffness or hardness
Over hours, the muscles of the affected limb may become firm or hard to the touch as they lose their blood supply. This change reflects ongoing damage to the muscle tissue.
Breathing difficulty or open-mouth breathing
Some cats develop laboured breathing or breathe with their mouths open, which may indicate fluid accumulation in the chest or worsening heart function. The pattern may worsen over time or remain steady.
Loss of appetite or lethargy
As the condition progresses, many cats become less interested in food and increasingly withdrawn. This change may reflect both the physical stress of the event and the underlying cardiac disease.
Complete paralysis of hind limbs
Both back legs may lose all voluntary movement, leaving the cat unable to reposition itself or walk. This bilateral pattern is common when the clot lodges at the point where the aorta divides to supply each leg.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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