I think most people know that high blood pressure is dangerous. It can lead to heart disease, heart attacks and stroke. Often there are no symptoms. It's called the silent killer for that reason.

So, we know what high blood pressure is and we know the risks. But do you know what the numbers mean? Belief.net Health has a very good explanation:

High blood pressure is abnormally high blood pressure with no known cause. Blood pressure measurements are read as two numbers. The higher number is called the systolic pressure. The lower number is called the diastolic pressure. Normal systolic pressure is 120 or less, and normal diastolic blood pressure is 80 or less.

High blood pressure is defined as systolic pressure greater than 140 and/or diastolic pressure greater than 90. People with systolic blood pressures between 120 and 139, or diastolic pressures of 80 to 89 are considered "pre-hypertensive" and need medical monitoring and lifestyle changes.

It's a good idea to get your blood pressure checked on a regular basis. Blood pressure monitors are available for home use as well. Don't be satisfied with just oe reading. Take three or more and average out the results to get close to the true reading.

The High Blood Pressure Connection issues this warning regarding hihg blood pressure:

It has been well documented that high blood pressure contributes to heart disease. This includes coronary artery disease and the resulting angina and heart attacks. Additionally, changes in heart muscle due to high blood pressure can lead to heart failure, a condition in which the heart cannot pump enough blood to meet the body's demands.