The two main heart sounds are caused by the valves slamming shut under back pressure of the blood as it is pumped into and out of the heart.
(The two main heart sounds; are caused; by the valves) (the valves slamming; shut; L:under back pressure of the blood; T:as it is pumped into and out of the heart) (it; is pumped; into and out of the heart)
The two main heart sounds the valves slamming it
are caused shut is pumped
by the valves
L:under back pressure of the blood T:as it is pumped into and out of the heart
into and out of the heart