Doppler signal from intracardiac blood flow

In this display, time is on the x-axis and flow velocity on the y-axis. By convention, flow away from the transducer is displayed below the line and that toward the transducer above the line; this spectral information can be displayed in real time (Doppler figure). The Doppler signal portrays the entire period of flow, ie, acceleration (a), peak flow (pf), and deceleration (d).