Background: Shorter duration of breastfeeding in infancy has been suggested to be associated with an increased risk of cardiovascular disease in adulthood. Early cardiovascular adaptations due to breastfeeding may explain these associations. Aim: To investigate whether breastfeeding affects left cardiac structures and blood pressure development in early childhood. Study design: Prospective cohort study from fetal life until the age of two years. Subjects: Information about the duration and exclusivity of breastfeeding was collected by questionnaires at the ages of 2,6 and 12 months in 933 children. Outcome measures: Left cardiac structures (left atrial diameter, aortic root diameter and left ventricular mass), fractional shortening and blood pressure at the ages of 1.5, 6 and 24 months. Results: No differences in cardiac structures, fractional shortening and blood pressure were observed between breastfed and non-breastfed children. Duration and exclusivity of breastfeeding were not consistently associated with any cardiac structure, fractional shortening, or blood pressure until the age of 24 months. Also, there was no association of breastfeeding with cardiac growth between 6 months and 24 months. All analyses were adjusted for child age and sex. Additional adjustment for child anthropometrics, maternal age, anthropometrics, family history, maternal cardiovascular risk factors, pregnancy or delivery complications, parity, socio-economic status, smoking status and alcohol consumption during pregnancy did not materially change the effect estimates. Conclusions: Our results do not support the hypothesis that early postnatal cardiovascular adaptations underlie the previously shown associations between breastfeeding and cardiovascular disease in adulthood. Further studies are needed to investigate whether and at what age the associations appear. (C) 2010 Elsevier Ireland Ltd. All rights reserved.