The heart and its nerve conduction, cardionector system. Frontal cut of the heart showing the 4 cardiac cavities: right and left atria, separated from the right and left ventricles by the tricuspid and mitral valves. The opening of the large vessels: the aorta the pulmonary trunk and the superior and inferior vena cava. The electrical conduction of the heart starts at the sinus node of Keith and Flack (orange), spreads to the auricles and atrioventricular node (yellow), then the bundle of His and the fibers of Punkinje (green)