The human heart is myogenic, which means the heart is capable of generating a cardiac contraction independent of nervous input. It also shows auto rhythmicity i.e. it can generate its own rhythm by the specialised muscles it has.
The SA node (sino-atrial node) is a specialised nodal cardiac tissue which is present in the right upper corner of right atrium. It can generate the maximum number of action potentials i.e.70-75 per min, and is responsible for initiating and maintaining rhythmic contractile activity of the heart.