Which part of the heart is responsible for initiating and maintaining its rhythmic activity?

Select the correct pathway for the transmission of cardiac impulses.

Provide the definition/explanation for the following heart valves:
$(1)$ $AV$ valve (Tricuspid)
$(2)$ Mitral (Bicuspid) valve

Heart beats are controlled by a nodal tissue which is composed of

Identify the correct statement.
$I$. The impulse of the heart beat originates from $SAN$.
$II$. Rate of the heart is determined by $SAN$.
$III$. Bundle of His/$AV$ bundle is present in the interventricular septum.
$IV$. Atrio Ventricular Node $(AVN)$ is situated in the lower left corner of the right auricle.
Choose the correct option.

In the heart, as the action potential reaches the $AV$ node from the $SA$ node, there is a delay of the action potential. This delay is important because: