Hypertension

There is no "ideal" blood pressure reading. However, there is a range of "normal" blood pressure readings. Generally, a reading that is less than 120 over 80 indicates that you don't need to worry. If either or both numbers are equal to or greater than 120 over 80 for an extended period of time, you have high blood pressure, or hypertension.
Hypertension is dangerous because it causes the heart to work extra hard. This strain contributes to heart attacks and stroke. When the heart is forced to work extra hard for an extended period of time, it tends to enlarge. A slightly enlarged heart can function well, but a significantly enlarged heart cannot. High blood pressure also causes damage to the arteries, causing arterial disease.
Hypertension can be treated. Mild cases of hypertension can be treated through behavior modification like changing diet and increasing exercise. More severe cases of hypertension require medications like diuretics, beta blockers, ACE inhibitors, and calcium channel blockers. Each type of chemical works differently in an attempt to bring blood pressure back into a normal range. For example, diuretics rid the body of excess fluids and salt while beta blockers reduce the heart rate and the heart's output of blood.
Please note that these are general statements about hypertension. For individualized information, it is essential that you consult with a medical professional.