Blood pressure is the force of blood pushing against the walls of the arteries with each heartbeat. It is a surge of blood throughout your body. We all need enough oxygen to provide our body tissues with energy. This is the primary job of the heart and blood vessels – pumping oxygenated blood from the lungs and dispersing it around the body. Having the right blood pressure is important: too high, or hypertension, causes stroke, heart attack, heart failure, and kidney disease after a while. Too low, or hypotension, can cause weakness, tiredness, lightheadedness, and fainting.