Diastolic blood pressure is the lower of the two numbers in a blood pressure reading (for example, the 80 in 120/80 mmHg). It represents the pressure in the arteries when the heart muscle is relaxing between beats (during diastole), before the next contraction. During this phase, the aortic and pulmonary valves are closed and the heart refills with blood.
Diastolic blood pressure reflects the minimum pressure maintained in the arterial system by the elastic recoil of the large arteries following each heartbeat. A normal diastolic blood pressure is below 80 mmHg. Values of 80 to 89 mmHg represent stage 1 hypertension, and 90 mmHg or above represents stage 2 hypertension.
In practice, both the systolic (upper) and diastolic readings matter for cardiovascular risk assessment, though elevated systolic pressure tends to be a stronger predictor of cardiovascular events in older adults, where large artery stiffness becomes the predominant problem.
Low diastolic blood pressure (below 60 to 70 mmHg) can also be clinically significant, particularly in patients with heart failure or coronary artery disease. The coronary arteries fill during diastole, so a very low diastolic pressure may compromise coronary blood flow, increasing the risk of myocardial ischaemia. For cardiac arrest survivors in critical care, maintaining adequate blood pressure (both systolic and diastolic components) is essential to support organ perfusion during recovery. Blood pressure targets in the post-arrest period are set by the intensive care team based on the patient’s individual circumstances.
« Back to Glossary Index