Saddle thrombus (aortic thromboembolism) in cats


  • A saddle thrombus is a blood clot that blocks blood supply to the back legs.
  • Symptoms appear suddenly and include severely painful, paralysed back legs.
  • A saddle thrombus is an emergency – contact your vet immediately if your cat is showing symptoms.
  • It’s important to start treatment as soon as possible to give your cat the best chance of recovery
  • Sadly, many cats don’t survive a saddle thrombus.
  • A saddle thrombus is sometimes referred to as an ‘aortic thromboembolism’, which simply means a clot travelling in the main artery (the aorta).

What is a saddle thrombus?

A saddle thrombus is a blood clot that cuts off blood supply to the back legs. The clot forms in the heart, gets pumped into the main artery (the aorta), then travels in the bloodstream until it reaches the junction leading to the arteries in the back legs. It lodges at the junction and cuts off blood supply to the legs. Without blood, the back legs become paralysed and extremely painful. The clot is called a ‘saddle thrombus’ because it sits like a saddle, across the two blood vessels that branch into the back legs.

If the clot is small, it may travel past the junction and lodge in a smaller back-leg artery. In this case, symptoms appear in just one leg.

Blood clots can also travel to other parts of the body, blocking blood flow to organs such as the kidneys, lungs or brain.

Illustration showing saddle thrombus

Click image to enlarge.


Saddle thrombi are most common in cats with heart disease. This is because cats with heart disease often develop large clots inside their heart that release small clots into the blood stream. Other, less common causes include hyperthyroidism and cancer.


Symptoms appear suddenly and include:

  • Severe pain (crying, fast breathing, hiding)
  • Being unable to stand / dragging one or both back legs (occasionally a front leg)
  • Licking or chewing the affected leg(s)
  • Firm muscles in the affected leg(s)
  • Affected leg(s) cold to the touch
  • Pale foot-pads in the affected leg(s) (can be difficult to tell if they are black).

When to contact your vet

Contact your vet straight away if you see any saddle thrombus symptoms.

You know your cat – if they don’t have the exact symptoms listed above but you are still concerned, it’s always best to contact your vet.


A saddle thrombus is a very serious condition that sadly, despite treatment, most cats don’t survive. Your cat will need hospitalisation for intensive treatment and nursing care.

Pain relief. Your vet will give your cat strong pain relief to help with the severe pain caused by a saddle thrombus.

Dissolving the blood clot. Your vet will use ‘clot-busting’ medicines to try to dissolve the clot. It can take 2-4 days for the clot to clear but sadly, many clots don’t respond to treatment.

Surgery. If the clot doesn’t dissolve, some specialist vets can operate to remove it, but it’s important to be aware that this surgery is very risky. The vessel that the blood clot sits inside is likely to be very small and difficult to access, and if the clot is successfully removed, the sudden release of blood into the leg can cause a condition called ‘reperfusion injury’. This is a very serious problem, which causes severe swelling in the leg, a release of toxins and often leads to death.

Physiotherapy. Your cat may receive physiotherapy if it’s not too painful for them.

Treating the underlying cause. Your vet will try to find out why your cat has developed a saddle thrombus and treat the condition accordingly e.g. heart disease, hyperthyroidism or cancer.


Sadly, outlook for a cat with a saddle thrombus is very poor - it’s an extremely serious condition that most cats don’t recover from.

Once your vet has an idea of why your cat has developed a saddle thrombus, they will be able to give you an idea of the likely outcome. Treatment is worth a try if your vet thinks your cat has a chance of responding, but sadly, it may necessary to put them to sleep if they don’t show signs of improving within 2-3 days, are in severe, uncontrollable pain or if your vet feels that their outlook is hopeless.

It’s important to be aware that a third of cats that recover from a saddle thrombus develop the condition again, and their symptoms may not completely resolve i.e. they may be left with some dysfunction in their back legs.

If your cat recovers from a saddle thrombus it’s likely they will need ongoing treatment for the rest of their life to prevent further blood clots forming, and also for any underlying problems such as heart disease or hyperthyroidism.

Home care

If your cat shows enough of an improvement to return home, your vet will advise you how to nurse them. This will include medication, hand feeding, toileting, physiotherapy and grooming.

You may find the following helpful:

How to give your cat a tablet


The best way to prevent a saddle thrombus is to make sure you have your cat regularly checked by your vet. This will ensure your vet notices any developing conditions i.e. heart disease, before they cause a clot. Booster vaccination appointments are a perfect time for a full health check for your cat.

If your cat has had a blood clot in the past, your vet may prescribe blood thinners, but there is still a high risk that another clot will form.


Treatment for a saddle thrombus is often very expensive due to the intensive treatment required.

When you welcome a new cat into your life, consider getting Cat Insurance straight away before any signs of illness start. This will give you peace of mind that you have some financial support if they ever get sick. 

It’s also very important to speak openly to your vet about your finances, the cost of treatment, as well as what you think is right for your cat. There are often several treatment options so if one doesn’t work for you and your pet then the vet may be able to offer another.

Published: August 2019

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.