BACKGROUND: Carbetocin is a synthetic oxytocin-analogue, which should be administered as bolus according to manufacturer's recommendations. A higher speed of oxytocin administration leads to increased cardiovascular side-effects. It is unclear whether carbetocin administration as short infusion has the same efficacy on uterine tone compared with bolus administration and whether haemodynamic parameters differ. METHODS: In this randomized, double-blind, non-inferiority trial, women undergoing planned or unplanned Caesarean section (CS) under regional anaesthesia received a bolus and a short infusion, only one of which contained carbetocin 100 mcg (double dummy). Obstetricians quantified uterine tone two, three, five and 10 min after cord-clamping by manual palpation using a linear analogue scale from 0 to 100. We evaluated whether the lower limit of the 95% CI of the difference in maximum uterine tone within the first five min after cord-clamping did not include the pre-specified non-inferiority limit of -10. RESULTS: Between December 2014 and November 2015, 69 patients were randomized to receive carbetocin as bolus and 71 to receive it as short infusion. Maximal uterine tone was 89 in the bolus and 88 in the short infusion group (mean difference -1.3, 95% CI -5.7 to 3.1). Bp, calculated blood loss, use of additional uterotonics, and side-effects were comparable. CONCLUSIONS: Administration of carbetocin as short infusion does not compromise uterine tone and has similar cardiovascular side-effects as a slow i.v. bolus. In accordance with current recommendations for oxytocin, carbetocin can safely be administered as short -infusion during planned or unplanned CS. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov NCT02221531 and www.kofam.ch SNCTP000001197.