<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> <P> Electrical signals arising in the SA node (located in the right atrium) stimulate the atria to contract . Then the signals travel to the atrioventricular node (AV node), which is located in the interatrial septum . After a delay, the electrical signal diverges and is conducted through the left and right bundle of His to the respective Purkinje fibers for each side of the heart, as well as to the endocardium at the apex of the heart, then finally to the ventricular epicardium; causing its contraction . These signals are generated rhytmically, which in turn results in the coordinated rhythmic contraction and relaxation of the heart . </P>

Which portion of the conduction system depolarizes spontaneously to initiate each heartbeat