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| How Your Heart
Works
HOW YOUR HEART WORKS
Your heart, which is about the size of your clenched fist, is made up of four
chambers: two on the left, and two on the right. Each of
the two upper chambers is called an atrium, and the two
lower chambers are called ventricles. The atria receive
blood from veins and the ventricles pump blood out to the
body. The left ventricle sends blood out to all parts of
the body, except the lungs; the right ventricle supplies
only the lungs with blood.
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The left
and right sides of the heart are separated by a wall
of muscle, called the septum. The valves allow blood
to flow in only one direction. When the atria fill
with blood from the veins returning to the heart,
the valves have higher pressure above than below,
and the atria contract, letting blood flow into the
ventricles. The filled ventricles then contract and
force the blood out through the mitral and tricuspid
valves.
The aortic and pulmonary valves open and snap shut,
letting blood into the aorta, and pulmonary artery.
As these valves snap closed, preventing blood from
returning to the ventricle, the sound they make is
what we call a heartbeat. This supplies every organ
in the body with life-sustaining oxygenated blood,
except the heart itself. The coronary arteries are
the heart's private circulatory system, fed directly
from the aorta.
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The two main coronary arteries, right and left, branch and divide into smaller and smaller tributaries. Heart muscle would soon die if a main coronary artery became blocked, and could not supply enough blood, but the smaller branches are capable of connecting with those of other arteries, providing what is called collateral circulation. The coronary arteries start from the aorta, and spread to many smaller branches that supply the heart muscles.
When plaque blocks these arteries, blood does not reach the muscles. Without oxygenated blood, muscles cannot contract to pump blood.
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