In women with heart disease (HD), the third stage of labour is managed with a reduced dose of oxytocin because it can have significant adverse cardiovascular effects. However, women with HD have high rates of postpartum haemorrhage (PPH); consequently, we designed a prospective study to investigate whether higher doses of oxytocin can be given safely and would reduce rates of PPH. We performed a single centre, prospective, cohort study comparing the standard 'low-dose' oxytocin infusion (10 U of oxytocin in 500 mL of normal saline given intravenously at 36 mL/hour for 4 hours (12 mU/min), n=29) to the low-dose infusion and an additional 2 U of oxytocin given over 10 min immediately after birth (n=30). Maternal blood pressure was measured every minute for 10 min, continuous ECG (Holter) monitoring was performed and any symptoms (chest pain, dyspnoea) were recorded. Total blood loss and serum troponins were measured at 12 hours. There were no cardiac symptoms, arrhythmias, change in the ST segment or increase in serum troponins. The fall in blood pressure and increase in heart rate were greater with the additional oxytocin, but neither were statistically or clinically significant. The blood loss was significantly less in women receiving additional oxytocin (505 vs 849 mL) and the proportion of women having a PPH was lower. The use of an additional 2 U of oxytocin for the management of third stage in women with HD had no cardiac consequences and was associated with a significantly lower blood loss. Further larger studies on a larger population of women with HD are needed. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.