Systolic blood pressure is the maximum arterial pressure during the cardiac cycle, occurring when the heart's ventricles contract (systole) to eject blood into the arteries. This pressure reflects the force exerted by the blood against the arterial walls during ventricular contraction, which is critical for ensuring sufficient blood flow to organs. Measuring systolic pressure provides essential information about cardiac function and vascular resistance. It is distinct from diastolic pressure, which represents arterial pressure during ventricular relaxation. Accurate assessment of systolic pressure is vital in diagnosing and managing conditions like hypertension and heart disease.

Reference: Harrison's Principles of Internal Medicine, Kasper et al., 20th Edition.