En español | Strokes can be mild or catastrophic, "but you can't tell the severity by the symptoms. That's why you have to move fast when even minor symptoms appear," says Walter J. Koroshetz, M.D., deputy director at the National Institute of Neurological Disorders and Stroke. "The longer blood flow is cut off to the brain, the more devastating the damage is," he says.

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Stroke symptoms usually develop suddenly and without warning, or they may occur on and off for a day or two.

The optimal window of treatment is about three hours from the onset of symptoms, so it's crucial to call 911 immediately if you suspect you or someone else is having a stroke.

"Wait-and-see should not be a part of the decision process," says Edward C. Jauch, M.D., of the Medical University of South Carolina. Some stroke victims may not be aware of their symptoms or may be unable to communicate, adds Jauch, who also is a member of the National Stroke Association's Professional Advisory Committee.

Two kinds of stroke

About 87 percent of all strokes are "ischemic," and occur when a blood clot blocks a blood vessel in the brain or an artery to the brain. If administered in time, clot busting drugs can help reduce the damage from this kind of stroke, so getting treatment quickly is critical.

The second type of stroke is "hemorrhagic," and occurs when a blood vessel in the brain breaks, causing bleeding in the brain. These strokes generally need to be treated in intensive care and may require surgery.

A mini-stroke, or "transient ischemic attack," is caused when blood to the brain is temporarily disrupted. Symptoms, the same as for major strokes, last for only an hour or so then vanish.

"If this happens, call your doctor or go to an emergency clinic. Don't just forget about it, " says Thomas Sweeney, M.D., of the Connecticut Vascular Center.

A mini-stroke, he says, can signal that a full-blown stroke is imminent — maybe just hours away. After a mini-stroke, the risk of a permanent stroke can be reduced if you go for medical help, says Sweeney. Treatment might include blood thinners to combat clotting, surgery to clear a blocked artery or treatment plans for underlying disorders, such as high blood pressure, high cholesterol, heart disease and diabetes.

Next: When to call 911.  >>