In the heart muscle there are special, electrically active cells for the formation and transmission of electrical impulses. A collection of such cells in the right atrium forms the sinus node, the "pacemaker" of the heart. From here, electrical impulses are regularly "fired" and transported to the muscle cells via special pathways (conduction system). The muscle cells "respond" to these electrical impulses with a contraction, i.e. they contract. The coordinated contraction of all the heart muscle cells produces the pumping motion of the heart (systole). An ECG can be used to show the development and course of the electrical impulses.
