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Umbilical cord clamping at birth has a major impact on an infant's cardiovascular system that varies in significance depending upon whether the infant has commenced breathing. As umbilical venous return is a major source of preload for the left ventricle during fetal life, recent experimental evidence has shown that clamping the umbilical cord severely limits cardiac venous return in the absence of pulmonary ventilation. As a result, cardiac output greatly reduces and remains low until breathing commences. Once the infant begins breathing, aeration of the lung triggers a large increase in pulmonary blood flow, which replaces umbilical venous return as the source of preload for the left ventricle. As a result, cardiac output markedly increases, as indicated by an increase in heart rate immediately after birth. Thus, infants born apnoeic and hypoxic and have their cords immediately clamped, are likely to have a restricted …