<Tr> <Th> FMA </Th> <Td> 9476 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node to cause contraction of the heart muscle . The pacemaking signal generated in the sinoatrial node travels through the right atrium to the atrioventricular node, along the Bundle of His and through bundle branches to cause contraction of the heart muscle . This signal stimulates contraction first of the right and left atrium, and then the right and left ventricles . This process allows blood to be pumped throughout the body . </P> <P> The conduction system consists of specialised heart muscle cells, and is situated within the myocardium . There is a skeleton of fibrous tissue that surrounds the conduction system which can be seen on an ECG . Dysfunction of the conduction system can cause irregular, fast, or slow heart rhythms . </P>

When does the atria contract on an ecg
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