The sinoatrial node (SAN), atrioventricular node (AVN), the conduction system the bundle of His and its branches, and the purkinje system are capable of spontaneous discharge. In addition under abnormal condition the myocardium also has the capability to discharge spontaneously. Each node, the conducting system as well as myocardium discharge at variable rate as indicated in the table below. SA node being the highest intrinsic rate, is the normal cardiac pacemaker .
| Tissue | Rate |
| SAN | 80-100 |
| AVN | 60-80 |
| Bundle of His | 40-60 |
| Myocardium | 20-40 |
Impulse originating from SAN spread to the atrium through internodal atrial pathway to AVN. From AVN, impulses spread to the ventricle through Bundle of His and the Purkinje fibre. The sequence of spread impulses are shown below.