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Around 85% of all strokes are due to a blockage cutting off the blood supply to the brain. This is called an ischaemic stroke.


A blockage can be caused by a blood clot forming in an artery leading to the brain or within one of the small vessels deep inside the brain. 

Blockages in the brain can also be caused by a clot moving through the blood stream from another part of the body. 

There are a number of reasons why blockages can form and cause an ischaemic stroke. These include:

  • Atherosclerosis, which occurs when fatty deposits build up on the inside walls of your arteries. They cause your arteries to become harder and narrower, making them more likely to become blocked. Sometimes, a blood clot forms on the fatty deposit. If this clot breaks away it can travel to the brain and cause a stroke.
  • Small vessel disease, which is when the tiny blood vessels deep within your brain are damaged.
  • Atrial fibrillation and other heart conditions, which can cause blood clots to form in your heart, which can then move through your blood stream up into your brain.
  • Arterial dissection, which occurs when tears develop in the lining of an artery and allow blood to get between the layers of your artery walls. This can happen for no clear reason or it can happen because of an injury to the neck.


A stroke is a medical emergency and if you have any stroke symptoms you need to call 999 immediately.

Ambulance paramedics are trained in stroke and will assess the person and take them to the right kind of hospital for treatment. This could be a hospital with a specialist stroke unit or a hyper-acute stroke unit.

A stroke unit has a range of trained professionals who are experienced in stroke care. 

The quicker your stroke is diagnosed and treated, the better your recovery will be.

If you have a suspected stroke, you should have a brain scan, within one hour if possible. A scan can help doctors decide on the right treatment for you. You will either have a computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan.


If your ischaemic stroke is caused by a blood clot, you may be given a clot-busting treatment known as thrombolysis.

Thrombolysis can break down and disperse a clot that is preventing blood from reaching your brain. However, for it to have the best effect, it needs to be given within four and a half hours of your stroke symptoms starting.

Thrombectomy is a treatment that removes the clot with a mechanical device. Only a small proportion of strokes are eligible for thrombectomy but it can have a big impact on reducing disability after a stroke.

Most people who have an ischaemic stroke will be given anti-platelet medication, which helps to prevent blood clots from forming.

After a stroke you will be checked for health conditions linked to stroke, such as atrial fibrillation, diabetes and high cholesterol. If you have any of these conditions you will be given treatment and advice.Ths is important to help reduce the chance of having another stroke.

Find out more

  • Ischaemic stroke - our guide with more information about how an ischaemic stroke is diagnosed and treated.
  • Find out more about ischaemic stroke on My Stroke Guide. As well as free access to trusted advice, information and support 24/7, My Stroke Guide connects you to our online community, to find out how others manage their recovery.