Arterial stiffening is the principal cause of increasing systolic pressure with advancing years and in patients with arterial hypertension. It is associated with progressive arterial dilation and is due to degeneration of the arterial wall, probably as a consequence of repetitive cyclic stress; it increases systolic pressure directly by increasing amplitude of the pressure wave generated by a given flow impulse from the heart and indirectly by increasing wave velocity so that wave reflection from the periphery occurs earlier, augmenting pressure in late systole. The first mechanism affects pressure in both the central and peripheral arteries, the second predominantly in the central arteries. Change in brachial systolic pressure with age underestimates the rise in systolic pressure in the aorta and left ventricle. Arterial stiffness is reduced passively with reduction in arterial pressure. Drugs have little or no direct effect on arterial stiffness but can markedly reduce wave reflection. In patients with stiffened arteries, reduction in wave reflection decreases aortic systolic pressure augmentation. The decreased systolic pressure in central arteries brought about by this mechanism is not detected when systolic pressure is measured in a peripheral (brachial or radial) artery but can be inferred from change in contour of the pressure wave recorded in peripheral arteries.