Which flow component is indicated by the arrows on this image?

The Doppler waveform shows pulmonary vein flow with several components. The arrows point to small reversed flow spikes just after the atrial contraction wave, which corresponds to the atrial reversal (AR) flow component. Atrial reversal occurs as blood briefly flows backward into the pulmonary veins during atrial contraction.

Ventricular reversal is not typically seen in pulmonary veins. Diastolic flow reversal is abnormal and usually not part of normal pulmonary vein flow. Systolic forward flow is the major forward component during ventricular systole.

This interpretation is standard in ASE guidelines on diastolic function assessment and pulmonary vein Doppler evaluation【12:ASE Diastolic Function Guidelines†p.85-90】【16:Textbook of Clinical Echocardiography, 6e†p.130-135】.