What is the function of valves in the heart?

$A$ heart murmur occurs due to a defect in:

The $SA$ node is located in

When do the 'lub' and 'dub' sounds occur during the cardiac cycle?
Lub $\quad$ $\quad$ $\quad$ Dub

$A$ specialised nodal tissue embedded in the lower corner of the right atrium,close to the atrioventricular septum,delays the spreading of impulses to the heart apex for about $0.1 \; sec$. This delay allows:

What is the first heart sound?