The aim of this study was to analyse the velocity profile of the systolic fraction of the pulmonary venous flow (PVF) in mitral regurgitation (MR). Three velocity profiles were identified in left superior pulmonary vein. Inversion of the systolic fraction of the PVF was specific for angiographic grade 4 MR (specificity 97%, sensitivity 100%). On the other hand, a decrease in this wave is much less specific for mild MR and depends on severe factors such as left atrial pressure, size and ejection fraction and the lack of atrial systole (as in atrial fibrillation or atrioventricular block). Therefore, inversion of PVF has a good positive predictive value for severe MR, but the interpretation of attenuation of this wave should take into consideration not only the MR but also left atrial pressure and compliance.