Spinal anaesthesia for elective caesarean section is associated with maternal hypotension, secondary to alteration of sympathetic tone and hypovolemia, in up to 70% of cases. Measurement of the subaortic variation in the velocity time integral (VTI) after passive leg raising allows prediction of fluid responsiveness. Our objective, in this prospective single-centre observational study, was to assess the ability of change in VTI after 45 degrees passive leg raising to predict hypotension after spinal anaesthesia. Ultrasound measurements were performed just before elective caesarean section. Anaesthesia, intravenous coloading and prophylactic vasopressor treatment were standardised according to current guidelines. We studied 40 women. Hypotension occurred in 17 (45%) women. The area (95%CI) under the receiver operating characteristics (ROC) curve for the prediction of spinal hypotension was 0.8 (0.6-0.9; p = 0.0001). Seventeen women had a change in VTI with leg elevation 8%, which was predictive for not developing hypotension, and 11 had a change 21%, predictive for hypotension. The grey zone between 8% and 21%, with inconclusive values, included 12 women. We suggest that cardiac ultrasound provides characterisation of the risk of hypotension following spinal anaesthesia at elective caesarean section, and therefore may allow individualised strategies for prevention and management.