 We explain strokes and why acting fast is so important. This is Mike. Today he's visiting his grandfather. They are playing chess, but suddenly Mike notices something very strange. His grandfather can't speak properly and his face looks different. What is going on? Take action. Mike's grandfather might be having a stroke, also called a brain attack. Strokes are the second largest cause of death worldwide, and also one of the largest causes of disability. They mainly happen in older people, but they can sometimes happen to younger people too. But what is a stroke? Our brain needs oxygen and nutrients, which it gets from our blood. When a stroke strikes, the blood can't get to where it needs to be. As a result, brain cells don't get enough oxygen and nutrients and become damaged or die. This can happen in one of two ways, either a blockage in the vessels that cut off the blood supply or bleeding in and around the brain. As we age, our arteries become harder and narrower and more likely to become blocked. However, medical conditions such as high blood pressure, atrial fibrillation and a regular heartbeat, in other words, or diabetes and lifestyle factors like smoking, drinking too much alcohol and not exercising can increase the risk of having a stroke. As our brain controls the whole body, there are a great variety of different effects of stroke, depending on the area of the brain that is damaged. They can include difficulties with speaking, seeing or hearing, balance and coordination problems, muscle weakness, confusion or memory loss. All these symptoms can occur suddenly within minutes. So how can Mike check if his grandfather might be having a stroke? By using the FAST test. The F stands for facial weakness. Can the person smile? Has their face fallen on one side? The A for arm weakness. Can the person raise both arms and keep them there? The S means speech problems. Can the person speak clearly and understand what you're saying? Is their speech slurred? And the T stands for time. If you notice any of these signs, it's time to call an ambulance immediately, even if the symptoms go away. The quicker a person gets to a specialist stroke unit, the quicker they will receive treatment, meaning more brain cells can be saved. Mike calls the ambulance right away. His grandfather gets the best treatment and makes a full recovery. And now they can play chess again, thanks to Mike and his FAST response.