Purkinje fibers primarily help in the contraction of which part of the heart?

The $SA$ node is located in

Blood enters the heart because of......

The heart beats continuously throughout life without fatigue because.....

$SA$ node (Sinoatrial node) ke baare mein sahi kathan chuniye:
$I$. Located at the right upper corner of the right atrium.
$II$. Heart of heart.
$III$. It initiates the rhythmic contractile activity of the heart.
$IV$. It is called the pace-keeper of the heart.
$V$. It is called the pacemaker of the heart.
Which of the following options contains the correct statements?

The valve present between the right ventricle and the pulmonary artery is: