The impulse of the heartbeat originates from:

Define / Explain the following terms:
$(1)$ Pacemaker
$(2)$ Erythroblastosis

If the heart of a mammal is injected with a $2\%$ $CaCl_2$ solution,then:

Which one is the correct route through which the cardiac impulse travels in the heart?

Analogy type questions:
$(1)$ Right atrium and right corner : $SA$ node :: Corner of right atrium : .......
$(2)$ First heart sound : $Lubb$ :: Second heart sound : ...........

The pacemaker of the heart is located in the .......