 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. Any 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 haze and purkinji cells. All these cells 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 everything, hence it does not show all its pacemaker activity. Only the sinoatrial node works as pacemaker of heart. However, if the sinoatrial node stops its activity, other auto-rhythmic components may take control of the auto-rhythmicity and heartbeat. However, such pacemakers slow down the rate of action or the rate of impulse generation. Such pacemakers are known as ectopic pacemakers. These ectopic pacemakers are two types. One is the atrioventricular node, which has a rhythmic discharge rate of 40 to 60 times per minute. And the other ectopic pacemakers are purkinji fibers, which can discharge from 15 to 40 times per minute. The reason is that if the ectopic pacemaker controls the heart, then the rate of heart is between 40 to 60 or 15 to 40 times per minute. Depending on the type of ectopic pacemaker, which controls the heart beat. Dear students, now we shall discuss the basis of self-excitation and auto-rhythmicity of pacemakers. What is the reason that the cells of the pacemaker themselves generate these electric impulses themselves? 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. But for this, the term that we use is necessary for resting. But the fibers of the sinoatrial node, the resting membrane potential of these are only between 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 cells, pacemaker cells, are naturally leaky to sodium and calcium ions. The flow of these sodium and calcium ions remains continuous. The effect of this is that sinoatrial nodal fibers undergo a steady depolarization, which is termed as pacemaker potential. Dear students, this pacemaker potential is gradually rising. The reason for this is that it reaches the threshold level and all our non-action potential is generated. This action potential is conducted to the whole of the cardiac tissue and contraction is caused.