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

What does the human heart $NOT$ possess?

What is the significance of the time gap in the passage of the action potential from the sino-atrial node to the ventricle?

State the location of the $SA$ node and the $AV$ node.

Left auricle receives pure blood from the:

Assertion : $Lub$ is a heart sound which is produced during each cardiac cycle.
Reason : It is associated with the closure of the tricuspid and bicuspid valves.