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When does our heart first start to beat? Until now, researchers thought that the first time our heart muscle contracted to beat was at eight days after conception in mice, which equates to around day 21 of a human pregnancy.

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Now, a team funded by the British Heart Foundation (BHF) at the University of Oxford has demonstrated earlier beating of the heart in mouse embryos which, if extrapolated to the human heart, suggests beating as early as 16 days after conception.

In the study, published in the journal eLife, researchers looked at the developing mouse heart and found that the muscle started to contract as soon as it formed the cardiac crescent – an early stage in heart development. In mice, this crescent forms 7.5 days after conception, which is equivalent to day 16 in the human embryo. Previously, it was thought that the heart started to contract a stage later, when the heart appears as a linear tube.

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