The normal heart is a strong, muscular pump a
little larger than a fist. It pumps blood continuously through the
circulatory system. Each day the average
heart "beats" (or expands and contracts) 100,000 times and pumps
about 2,000 gallons of blood. In a
70-year lifetime, an average human heart beats more than 2.5 billion
system is the network of
elastic tubes through which blood flows as it carries oxygen and
nutrients to all parts of the body. It includes the heart, lungs,
, arterioles (small arteries), and
capillaries (minute blood vessels). It
also includes venules (small veins) and veins, the
blood vessels through which blood flows as it returns to the heart.
If all these vessels were laid end-to-end, they would extend for
about 60,000 miles far enough to encircle the earth more than
The circulating blood brings oxygen and
nutrients to all the organs and tissues of the body, including the
heart itself. It also picks up waste products from the body's cells.
These waste products are removed as they're filtered through the
kidneys, liver and lungs.
What is the
structure of the heart?
The heart has four chambers. The upper two are
the right and left atria ; the lower two, the right and left
. The heart also has four valves that open
and close to allow blood to flow in only one direction when the heart
Echocardiographic image of the heart
The four heart valves are:
- the tricuspid valve, located
between the right atrium and right ventricle (RV);
- the pulmonary or
pulmonic valve, between the
right ventricle and the pulmonary artery;
- the mitral valve (MV), between the left
atrium (LA) and left ventricle; and
- the aortic valve (AV), between the
left ventricle (LV) and the aorta. Each valve has a set of flaps (also
called leaflets or cusps).
The mitral valve has two flaps; the others have
three. Under normal conditions, the valves permit blood to flow in
only one direction. Blood flow occurs only when there's a difference
in pressure across the valves that causes them to open.
How does the heart
The heart pumps blood to the lungs and to
all the body's tissues by a sequence of highly organized contractions
of its four chambers.
For the heart to function properly, the four
chambers must beat in an organized manner. This is governed by the
electrical impulse. A chamber of the heart contracts when an
electrical impulse or signal moves across it. Such a signal starts in
a small bundle of highly specialized cells located in the right
atrium the sinoatrial
node (SA node), also
called the sinus node.
A discharge from this natural "pacemaker" causes the
heart to beat. This pacemaker generates electrical impulses at a
given rate, but emotional reactions and hormonal factors can affect
its rate of discharge. This allows the heart rate to respond to
What are the warning signs of heart attack?
What is angina?
What is stroke?