The impulse for heart beat is originated in SA node. It is known as the pace maker of heart and situated in upper right corner of right atrium. The electrical impulses generated by SA node are conducted to Atrio Ventricular or AV node. From the AV node, the impulses are transmitted to AV bundle, known as bundle of His which convey the impulses of contraction to the apex of myocardium.
The impulses cause the Purkinje fibres to sweep upwards and outwards which results in pumping of blood into aorta and pulmonary artery. So, the correct sequence of propagation of cardiac impulse is SA node, AV node, Bundle of His, Purkinje fibres.

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