To evaluate the differences in shape and phase lag of the flow velocity curves in the superior (SVC) and inferior (IVC) venae cavae and the hepatic vein (HV), Doppler echocardiographic examination was performed in 40 healthy adults (aged 20 to 67 years, mean SD:, 39±12 years). Flow velocity patterns in each vein were characterized by 4 major deflections: S wave, a systolic forward flow; D wave, a diastolic forward flow; A wave, a small backward flow or reduction of diastolic forward flow due to atrial contraction: and O wave, a small back-ward flow or reduction of forward flow after the second heart sound. Except for a reduced phasic flow in a collapsed IVC, the venous flow velocity recordings in each vein demonstrated very similar pulsatile patterns and small differences in mean time lags of less than 50 msec. In general, the lowest values of peak A/peak S, peak O/peak S and peak D/peak S were observed in HV flow and the highest in IVC flow. Backflows of A and O waves were prominent in HV flow, but small and least frequent in IVC flow. These data suggest that the baseline of the central venous flow recordings might shift downward in HV flow and upward in IVC flow. However, even if both the baseline shift and amplitude of the flow curve were normalized in each venous flow velocity curve, apparent differences in shape of the flow velocity curves would remain. We concluded that the characteristics and differences of each central venous flow velocity pattern should be noted in studies of these areas.