This chapter discusses properties of cardiac muscle, which can be easily understood in light of the structural features and electrophysiology. The capability to contract even in the absence of neural control is called automaticity. Rhythmicity is conferred on the heart by the pacemaker tissue. Refractory period is the period during which a stimulus fails to evoke a response. In a beating heart, if an external stimulus is applied during contraction, there is no response irrespective of how strong the stimulus is. Since a fresh action potential has to be associated with every mechanical response, the mechanical responses of cardiac muscle cannot be merged. Since the refractory period is related to the duration of contraction, it is dependent on the heart rate. During the relaxation period, cardiac muscle is in the relative refractory period. The junction of the sinus venosus and atria can be easily blocked by tying a knot around it.