Strokes occur when blood flow to brain tissue is compromised. This is most commonly caused by atherosclerosis. This disease occurs in all humans to some extent, but is accelerated by certain co-morbidities (the presence of more than one health condition) or risk factors. There are some risk factors that cannot be modified, such as age, gender, heredity and ethnicity, that have influence on the rate of progression of this disease. There are also modifiable risk factors that create a predisposition to stroke such as high blood pressure, diabetes, high cholesterol, smoking, obesity, cardiac disease, lack of exercise and atrial fibrillation. If these health issues are identified and treated, the risk for stroke can be greatly reduced.