 Dear students, In this topic, we shall discuss the Autorhythmicity of pacemakers. Autorhythmicity is the ability of certain cardiac cells to spontaneously and repetitively generate an electrical impulse without a stimulus from the nervous system. Many cardiac cells that can generate an impulse and can maintain heart rate are known as pacemakers. Such cardiac cells include the sinoatrial node, cells of the atrioventricular node, the bundle of his and Purukinji cells. They have the ability to generate impulses. However, the rhythmical discharge of sinoatrial node is faster than all other impulse-generating parts. That is, it generates impulses at a rate of about 70 to 80 times per minute. So, sinoatrial node is virtually always the pacemaker of a normal heart. It dominates all other pacemakers because it does not show all its activity. The sinoatrial node is the pacemaker of a normal heart. However, if the sinoatrial node stops its activity, other auto-rhythmic components may take control of the auto-rhythmicity and heart beat. So, sinoatrial node is the pacemaker of a normal heart, the bundle of his and Purukinji cells. The rhythmical discharge rate is 60 times per minute, and other ectopic pacemakers are Purukinji fibers, which can discharge up to 15 to 40 times per minute. Now, we shall discuss the basis of self-excitation and auto-rhythmicity of pacemakers. What is the reason that the cells of pacemakers themselves generate these electric impulses? The reason for this is that there is no stable resting membrane potential in the cells of pacemakers. If they do not have stable resting membrane potential, then there is no resting membrane potential. However, the term used for this is necessary for resting, but the fibers of the sinoatrial node have a resting membrane potential of only minus 55 to minus 60 millivolts. In comparison, the other ventricular muscle fibers have a resting membrane potential of minus 85 to 90 millivolts. The cause of this less negative resting membrane potential is that the cell membranes of these pacemaker cells are naturally leaky to sodium and calcium ions. The effect of these sodium and calcium ions is that sinoatrial nodal fibers undergo a steady depolarization, which is termed as pacemaker potential. Dear students, this pacemaker potential is gradually rising and all our non-action potential is generated. This action potential is conducted to the whole of the cardiac tissue and contraction is cost.