During a stroke, every second counts. Two million brain cells die every minute. There's no test that can tell paramedics that someone is definitely having a stroke, so treatment is often delayed.
Research could be about to change that. Hear both sides of the story from stroke survivor Bill and researcher Chris.
From ambulance crew to stroke patient - Bill's story
For 30 years, Bill worked in an ambulance, then he was the one fighting for his life.
'I knew it could be a stroke, and I was scared for my life,' Bill says. 'I spent four weeks in hospital. I had paralysis down my left side.
When I went home, I realised life would never be the same again. I couldn't even get up and down the stairs. My stroke left me with many difficulties, and I know it can be far more devastating for other people. That's why I want to help more people whose lives are shattered by stroke.'
This test could save lives - Chris
'I've been involved in stroke research for 20 years. Now I'm working on an exciting study to develop a finger-prick test, which could help paramedics recognise stroke.
The first few hours after someone has a stroke are critical. For many patients, the effects of stroke can be less severe if they get the right emergency treatment quickly.
Each stroke is different and symptoms can vary. The FAST test can help, but it's still hard for paramedics to know if someone is having a stroke. This test aims to change that.'
Ambulance crews will be able to identify people they think are having a stroke and take them to a specialist stroke unit right away. This means they'll be able to get the correct emergency treatment sooner, giving them a higher chance of survival and a better recovery.'