Background: It is not known whether the optimal Atrioventricular delay (AV _opt) varies between left ventricular (LV) pacing site during endocardial biventricular pacing (BiVP) and may therefore needs consideration. Methods: We assessed the haemodynamic AV _opt in patients with chronic heart failure undergoing endocardial LV lead implantation. AV _opt was assessed during atrio-biventricular pacing (BVP) with a “roving LV lead”. Up to four locations were studied: mid lateral wall, mid septum (or a close alternative), site of greatest haemodynamic improvement and LV lead implant site. The AV _opt was compared to a fixed AV delay of 180ms. Results: Seventeen patients were included (12 male, aged 66.5 +/- 12.8 years, ejection fraction 26 +/- 7%, 16 left bundle branch block or high percentage of right ventricular pacing (RVP), QRS duration 167 +/-27 ms). In most locations (62/63), AV _opt increased systolic blood pressure during BiVP compared with RVP (relative improvement 6 mmHg, IQR 4-9mmHg). Compared to a fixed AV delay the haemodynamic improvement at AV _opt was higher (1mmHg, IQR 0.2-2.6mmHg, p<0.001). Within most patients (16/17), we observed a difference in AV _opt between pacing sites (median paced AV _opt 209 ms, IQR 117-250). Within this range, the haemodynamic impact of these differences was small (median loss 0.6 mmHg, IQR 0.1-2.6mmHg). Conclusion: Within a patient, different endocardial LV lead locations have slightly different haemodynamic AV _opt which are superior to a fixed AV delay. The haemodynamic consequence of applying an optimum from a different lead location is small.