Research has shown that parental smoking, particularly maternal smoking during pregnancy, greatly increases the risk of SIDS for a baby. However, the reason for this has never been properly explained. In newborn babies there is a temporary change in the electro-physiology of the heart which reverts to normal in the vast majority of cases by 6 months of age. If there is a delay in reverting to normal, it may lead to abnormal rhythm of the heart pump and perhaps expose the infant to sudden death. This research group will examine the possibility that the babies exposed to carbon monoxide in the womb (that is, whose mothers smoke) may not make this important move back to normal at the same time as babies whose mothers do not smoke.