What Is a Heart Attack?
How the heart works
You don t need a science degree - or even an O-level
in biology - to understand the mechanics of a heart
attack. It really is very simple.
First， a word about the circulation of the blood. The
heart is a pump which sends blood on its way through
the body. Blood goes to the lungs to pick up oxygen
from the air we breathe. This bright red oxygenated
blood is then conveyed round the body in the arteries
and returns to the heart， with the oxygen used up， via
the veins as dark red， de-oxygenated blood. Then the
cycle starts all over again.
Figure 1 is a drawing of the four chambers that make
up the human heart， showing the direction of the blood
flow.
The walls of these chambers are composed of a
special kind of muscle which does not tire. Each side
of the heart， left and right， has a thin-walled chamber
called an atrium， which lies over a much bigger and
stronger chamber called a ventricle. Each atrium is
separated from its corresponding ventricle， which en-
sures that the blood flows in one direction only. The
i right atrium is separated from the right ventricle by the
tricuspid valve; while the left atrium is separated from
the left ventricle by what is called the mitral valve，
because it looks like a bishop s mitre. Notice also that
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