The FAST test tells you whether someone is having a stroke right now

A stroke happens when blood flow to the brain stops, usually because a clot blocks an artery or a blood vessel ruptures. You have a narrow window—the first three to four and a half hours—when treatment can prevent permanent brain damage or death. The FAST test is the standard way to spot a stroke in progress: it takes less than a minute and tells you whether to call 911 immediately.

FAST stands for Face, Arms, Speech, Time. If you see any one of these signs, call 911 right away. Do not wait to see if it gets better. Do not drive the person to the hospital yourself. Call 911 and tell them you suspect a stroke—they will get an ambulance there faster and alert the hospital so a stroke team is ready.

Key Takeaways

  • The FAST test—Face drooping, Arm weakness, Speech difficulty, Time to call 911—catches most strokes in the critical window when treatment works best.
  • Some strokes cause no obvious symptoms at first; vision loss in one eye, sudden dizziness, or loss of balance can be stroke signs even without facial drooping.
  • Call 911 immediately if you see any stroke sign; do not drive or wait to see if symptoms pass.
  • The first three to four and a half hours after stroke onset are when clot-busting drugs and other emergency treatments prevent the most damage.
  • Write down the exact time the person first showed symptoms, because doctors need to know how long ago the stroke started.

Face drooping: what to look for

Ask the person to smile. In a stroke, one side of the face often droops or feels numb. The smile may look uneven—one corner of the mouth pulls up more than the other, or the mouth sags on one side. The person may not notice it themselves.

Drooping can be subtle. You might see it only when they smile, frown, or try to raise their eyebrows. If you are not sure, ask them to show their teeth or puff out their cheeks. Asymmetry on one side of the face is a red flag. Call 911 if you see it.

Arm weakness: how to test it

Ask the person to raise both arms in front of them, palms up, and hold them there for a few seconds. In a stroke, one arm often drifts downward or cannot lift at all. The person may not feel the weakness themselves—they might think they are holding their arms level when one is actually dropping.

Weakness can affect the leg too. Ask them to stand on one leg or walk a few steps. If one side of the body feels heavy, numb, or weak compared to the other, that is a stroke sign. Do not assume they are just tired or clumsy.

Speech difficulty: what counts as abnormal

Ask the person to repeat a simple sentence, like "The sky is blue" or "You can't teach an old dog new tricks." Stroke speech problems sound like slurring, mumbling, or words that do not come out right. The person may know what they want to say but cannot say it clearly. They may also have trouble understanding what you say to them.

Speech changes happen suddenly in a stroke. If someone has always had a slight accent or a speech pattern you know, that is normal. But if their speech changes right now—becomes slurred, slow, or hard to follow—that is a warning sign. Call 911.

Silent stroke signs that do not show up on the FAST test

Some strokes do not cause face drooping, arm weakness, or speech problems. They may damage parts of the brain that control vision, balance, or coordination instead. These silent strokes are easy to miss, but they are still emergencies.

Watch for sudden vision loss in one eye (the world goes dark or blurry on one side), sudden severe dizziness that makes the room spin, sudden loss of balance or coordination, sudden severe headache unlike any headache before, or sudden numbness or tingling on one side of the body. Any of these can be a stroke. Call 911 if they happen suddenly, even if the person can still talk and move normally.

What to do in the first minutes

Call 911 immediately. Tell the dispatcher you think someone is having a stroke. They will ask you questions and may give you instructions—follow them. Do not hang up until they tell you to.

Write down the exact time the person first showed symptoms. Doctors need to know how long ago the stroke started because it changes which treatments are possible. If the person was asleep when the stroke happened, write down the last time you know they were normal.

Do not give the person food, drink, or medication. Do not move them unless they are in immediate danger. Keep them calm and lying down. If they vomit, turn their head to the side so they do not choke. Stay with them until the ambulance arrives. Bring any medications they take regularly, their insurance card, and their ID.

Why the first few hours matter

A clot-busting drug called tPA (tissue plasminogen activator) can dissolve a blood clot and restore blood flow to the brain, but only if given within four and a half hours of when the stroke started. The sooner it is given, the better it works. Some newer treatments can help even up to 24 hours after a stroke starts, but they work best in the first hours too.

Every minute counts. Brain cells die when they do not get blood. The longer you wait, the more damage happens and the fewer treatment options remain. This is why calling 911 immediately—not waiting to see if it gets better, not driving yourself—makes the difference between recovery and permanent disability.

Frequently Asked Questions

What if I am not sure whether it is a stroke?

Call 911 anyway. It is better to call and be wrong than to wait and be right. Paramedics can assess the person and decide whether to go to a stroke center. Hospitals see many false alarms and do not penalize you for calling when you are unsure.

Can a stroke happen without any warning signs?

Most strokes have warning signs, but some people have small strokes (sometimes called TIAs or transient ischemic attacks) that cause symptoms that go away on their own within minutes or hours. These are still emergencies—they mean another, larger stroke is likely coming soon. Treat any sudden neurological change as a stroke until proven otherwise.

What if the person refuses to go to the hospital?

Call 911 anyway. Paramedics can assess them and transport them even if they refuse. A person having a stroke may not realize how serious it is or may have impaired judgment from the stroke itself. Do not let refusal stop you from getting help.

Is there anything I should do while waiting for the ambulance?

Keep the person calm and comfortable. If they are conscious and can swallow safely, you can let them sit or lie down. Do not give them anything to eat or drink. If they lose consciousness, turn them on their side so their airway stays open. Note the time and any details about what happened to tell the paramedics.

Can younger people have strokes?

Yes. Strokes are less common in younger adults, but they happen—especially in people with high blood pressure, diabetes, heart problems, or who smoke. The FAST test works the same way regardless of age. Do not assume someone is too young to be having a stroke.