A comparison of restrictive versus liberal transfusion thresholds to correct anaemia after cardiac surgery showed no differences in morbidity and total health-care costs. Patients allocated to a restrictive transfusion threshold (haemoglobin level <7.5 g/dl, n = 1,000) or a liberal threshold (haemoglobin level <9 g/dl, n = 1,003) had similar rates of the primary outcome of serious infection or ischaemic events within 3 months (35.1% vs 33.0%; OR 1.11, 95% CI 0.91–1.34, P = 0.30). Mortality was higher in the restrictive-threshold group than in the liberal-threshold group (4.2% vs 2.6%; HR 1.64, 95% CI 1.00–2.67; P = 0.045). Total health-care costs up to 3 months after surgery were similar in the two groups. Although restrictive thresholds require fewer units of red blood cells, the increased mortality in the restrictive-threshold group observed in this study raises concerns.