Pulse wave Doppler, also called pulsed wave or PW Doppler, is an ultrasound technique that measures blood flow velocity at a specific, user-selected location within the body. The sonographer places a small sample volume (gate) at the desired depth and angle within a vessel, and the machine sends pulses of ultrasound and listens for the returning Doppler-shifted echoes from that precise location. This provides depth-specific velocity information displayed as a spectral waveform showing how velocity changes over the cardiac cycle. The main limitation of pulse wave Doppler is aliasing — when flow velocities exceed the Nyquist limit (half the PRF), the waveform wraps around the display. For measuring very high velocities, continuous wave Doppler is used instead. Pulse wave Doppler is fundamental to virtually every vascular and cardiac Doppler examination.