What happens when you have a stroke?

A stroke happens when a blood vessel in your brain: Gets blocked and stops the flow of blood to the brain. This is called an ischemic stroke.

What is a stroke?

A stroke happens when a blood vessel in your brain gets blocked and stops the flow of oxygenated blood to the brainThis is called an ischemic stroke.

Picture of ischemic stroke. Source: National Heart, Lung and Blood Institute, National Institutes of Health

Bursts or bleeds in or around the brain. This is called a hemorrhagic stroke.

Picture of hemorrhagic stroke. Source: National Heart, Lung and Blood Institute, National Institutes of Health

What happens during a stroke?

Blood brings oxygen and nutrients to the body.  A burst or blocked blood vessel stops blood from reaching some parts of the brain. Blood that does not start flowing back to the brain within minutes can cause damage to the brain and the parts of the body it controls. The effects of a stroke will depend on where and how much of the brain was damaged and can affect how you think, see, move, feel and/or speak.  Learn about the functions of the brain.

Some strokes happen while people are asleep.  If you wake up with any of the following symptoms of a stroke, get medical help right away.    

  • numbness or weakness on one side of the body   
  • drooping of the face  
  • slurred or jumbled speech  
  • changes in vision, such as blurred or double vision  
  • sudden severe headache, usually with some of the other signs  
  • problems with balance  

What is a Transient Ischemic Attack (TIA)? 

Transient Ischemic Attack (TIA) happens when there is a temporary stoppage of blood flow and oxygen to the brain. The symptoms are like a stroke but only lasts less than 24 hours. This is often called a mini-stroke. A TIA is an important warning sign of a possible stroke. It is a medical emergency that needs to be assessed and treated right away. Symptoms of a TIA may include:

  • temporary weakness or numbness
  • slurred speech, or
  • trouble seeing clearly

What causes a stroke?

A stroke often happens without warning signs. 

There are some things that make it more likely that someone will have a stroke:

Risk factors for stroke can be divided into two categories: risk factors you can’t change (non-modifiable risk factors) and risk factors you can change (modifiable risk factors).  Modifiable risk factors can be controlled by medications, medical treatment, or lifestyle changes. Non-modifiable risk factors cannot be changed.

Modifiable Risk Factors

  • Hypertension
  • Hypercholesterolemia
  • Diabetes
  • Atrial fibrillation
  • Sleep apnea
  • Being overweight or obese
  • Physical inactivity
  • Smoking
  • Excessive alcohol and drug abuse
  • Stress

Non-Modifiable Risk Factors

  • Advanced age
  • Gender
  • Family and medical history
  • Ethnicity
  • Prior stroke or TIA

Signs of a stroke

Are there warning signs before a stroke happens?

For most people a stroke happens suddenly. The signs of a stroke are:

Stroke is a medical emergency.  Spot a stroke – act F.A.S.T

If you notice any of these warning signs, call 911 right away!

Credit: Northwestern Ontario Regional Stroke Network

Brain Hemispheres

Functions of the brain

The brain is divided into two large halves called hemispheres.



Do I know the types of tests that the doctor has ordered?



Commonly asked questions about stroke-related medications.

Stroke prevention clinics

Stroke Prevention Clinics

Stroke prevention clinics provide early assessment, treatment and education to people who have had a transient ischemic attack (TIA) or stroke, their families and caregivers.

Healthcare Team

Health Care Team

A list of health professionals that may care for you.

Having read the information in this section, consider the following:

  • Do I know what kind of stroke I had?
  • Do I know what caused my stroke?
  • Do I know what the symptoms of a stroke are?
  • Will I know what to do if I have symptoms of a stroke?
  • Do I have a plan in place if I have an emergency?

Where to get more information, help and support:

Heart and Stroke Foundation

Toronto Central Healthline

Aphasia Institute