Blood pressure is expressed as one number over another.
The top number is the systolic pressure, or the pressure on arteries as the heart contracts or beats. The bottom number is the diastolic pressure, or the pressure on arteries as the heart relaxes between beats. Unfortunately, most people with high blood pressure have no symptoms - this is why hypertension is called the silent killer. Occasionally high blood pressure can cause a headache or dizziness, but this is not common. Sometimes, the first sign of hypertension is a stroke.