['During off-pump coronary artery bypass (OPCAB), the displacement of the heart causes mitral regurgitation. We hypothesized that patients with impaired left ventricle (LV) function would be more prone to develop mitral regurgitation, due to further LV end-diastolic pressure elevation and mitral annulus distortion. Therefore, in this study, we examined the relationship between LV function and the severity of mitral regurgitation.', 'We studied 41 patients undergoing elective OPCAB. LV function was evaluated by LV ejection fraction (LVEF), serum brain natriuretic peptide (BNP) levels, the Tei index (myocardial performance index) and mitral inflow propagation velocity (Vp).', 'Among all of the anastomoses performed mitral regurgitation was most severe during anastomosis of the left circumflex artery (LCX) territory (P < 0.001). Twenty-five patients (61%) had no to mild mitral regurgitation during anastomosis of the LCX territory (M-MR group) and 16 patients (39%) had moderate to severe mitral regurgitation during anastomosis of the LCX territory (S-MR group). There were significant differences between these groups in preoperative serum BNP levels (median, 26 pg.ml(-1) interquartile range [IQR, 14 to 75 pg.ml(-1)] versus median, 173 pg.ml(-1) [IQR, 91 to 296 pg.ml(-1)]; P < 0.001), Tei index values (median, 0.35; [IQR, 0.27 to 0.41] versus median, 0.53 [IQR, 0.47 to 0.57]; P < 0.001), and Vp (median, 63 cm.s(-1); [IQR, 57 to 72 cm.s(-1)] versus median, 47 cm.s(-1); [IQR, 40 to 57 cm.c(-1)]; P = 0.008), while there was no significant difference in LVEF between the patients in the M-MR group and those in the S-MR group.'] Is the degree of newly emerging mitral regurgitation during off-pump coronary artery bypass predicted by preoperative left ventricular function?