RECENT STUDIES of cardiac function have drawn attention to vascular impedance as ventricular afterload.'-' In comparisons of changing load under different circumstances, vascular impedance is usually expressed as characteristic impedance.3 5 7-9 Characteristic impedance has been used also as an index of arterial distensibility and this (when expressed in appropriate units) has been shown to change in different disease conditions with different drugs and with increasing age. , [9][10][11][12][13][14][15] Characteristic impedance of an arterial segment is directly related to regional arterial pulse wave velocity (PWV). 0 Regional PWV can be determined from the time delay between the foot of pulse waves recorded in proximal and distal sites and the distance between recording sites. Hence valuable information on left ventricular load and on systemic arterial distensibility