Origin of heartbeat - SAN (Sino-atrial Node)/Pacemaker

Conduction Pathway -

SAN (Sino-atrial Node)/Pacemaker ---> AVN (Atrio-ventricular Node)/Pacesetter ---> AV bundle (Atro-ventricular bundle) ---> Bundle of His ---> Purkinje Fibres

Remember that although all the heart muscles have the ability to generate impulses that trigger cardiac contractions, the SAN initiates it, as it generates the max number of action potentials (70-75 per minute), and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.