The first step in understanding high blood pressure is learning what your numbers mean. Blood pressure is measured with two numbers: systolic (the higher number) and diastolic (the lower number) (e.g., 120/80 mmHg): Systolic pressure occurs when your heart contracts. Diastolic pressure occurs when your heart relaxes and fills with blood. Blood pressure is measured using millimeters of mercury (mmHg), a standardized measurement of pressure. The higher your systolic or diastolic blood pressure – and the longer it stays high – the greater the potential damage to your blood vessels. Always consult with your health care provider before making changes to your blood pressure management plan.