Two fundamental properties of protoplasm: contractility and conductivity, are brought to a high degree of development in muscular tissue. The rhythm of the mammalian heart is initiated and regulated by fibers that have become specialized to conduct the electrical impulse. These fibers comprise the impulse conduction system of the heart, and they are capable of the conduction of an impulse at a faster rate than the rest of the myocardium, whose fibers are specialized for contraction, which has earned them the terminology of “working myocardium”. Conduction tissue has the property of automaticity, which is defined as the ability of a cell to depolarize spontaneously during the diastolic interval and to reach the threshold potential, thus generating an action potential. The conducting cells have a lower internal resistance and a higher conductance than the tension generating cells of the myocardium, which are specialized for contraction. This tissue shows a prepotential rise of the baseline, so that the cells are already partially depolarized.