Baroness Thatcher died after suffering from a stroke - a condition which kills around 45,000 people every year in the UK.
Strokes are the third largest cause of death, after heart disease and cancer.
All strokes result in damage to the brain, either due to blocked arteries or bleeding from ruptured blood vessels.
Ischaemic strokes, which account for more than 80% of all strokes, occur when the blood supply is stopped due to a blood clot.
Haemorrhagic strokes happen when a weakened blood vessel supplying the brain bursts and causes brain damage.
The risk of stroke rises significantly with age. And 40,000 of those who die each year are over the age of 75, according to the Stroke Association.
The condition affects 152,000 people in the UK every year. The brain damage caused by strokes means that they are the largest cause of adult disability in the UK.
Jon Barrick, chief executive of the Stroke Association, said: "We are deeply saddened to hear about the death of Baroness Thatcher from a stroke. Our thoughts are with her family at this very sad time.
"Around 150,000 people have a stroke every year in the UK and approximately one in five is fatal.
"Thanks to improvements in hospital care and better recognition of the symptoms through the Fast campaign many more people are surviving a stroke and are going on to make a good recovery.
"Today there are over one million people living in the UK with the after effects of the condition and although a stroke happens in an instant the effects can often last a lifetime."
The "Fast" campaign urges people to look out for the following signs and call 999 if they spot a single one:
Facial weakness - can the person smile? Has their mouth or eye drooped?
Arm weakness - can the person raise both arms?
Speech problems - can the person speak clearly and understand what you say?
Time - to call 999 for an ambulance if any one of these signs occurs.