What is blood pressure? Blood pressure is the force of your blood against your artery walls. When you have your blood pressure checked the reading has two numbers; one on top and one on bottom.The top number is your systolic pressure. This is the force of your blood in your arteries when your heart beats. The bottom number is your diastolic pressure. This is the force of your blood in your arteries when your heart relaxes in-between beats. Normal blood pressure would be a reading of 120/80 or lower. High blood pressure would be a reading of 140/90 or higher. If you have high blood pressure you are at a greater risk of a stroke or heart and kidney disease.