It's the nation's third largest cause of death.
700,000 Americans have a stroke each year.
But would you know the warning signs?
Betty Modaressi is recovering from a stroke that came from nowhere last week.
Now she realizes there may have been warning signs.
"I had several little what my mother calls 'spells' where I would try to say something and something else would come out," said Modaressi.
Across the country, someone has a stroke every 40 seconds.
But cardiologist Cameron Haery says people often don't know the symptoms or simply ignore them.
"Sudden and severe unexpected headache, dizziness or loss of your balance, or your gait, unable to walk in a straight line," said Haery.
Stroke patients may also have slurred speech or numbness in an arm or leg.
And Dr. Haery says while almost everyone gets a headache once in a while, it's a combination of symptoms that points to trouble.
"For example if you have a sudden or severe headache that is new and it is associated with weakness or numbness in an arm or a leg," said Haery.
And if it is a stroke, time is critical.
"You can see its a nice long black tube. That's the dye in the blood flow going to the brain, but here there's a blockage," Haery said.