Generally, a reading that is less than 140 over 90 indicates that you don't need to worry. If either or both numbers are equal to or greater than 140 over 90 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.