The heart is a hard-working muscle about the size of a fist.
It is located under your ribcage between the lungs. The heart pumps a constant
supply of blood throughout your body. The blood carries oxygen and nourishment,
the fuel your cells need for daily living.
The heart is made up of four chambers – two atria and
two ventricles – separated by a wall and valves. They are like four rooms,
two upper and two lower, with doors between each upper and lower room. With
each beat of the heart, the blood in the atria flows through the doors, or valves,
to the ventricles. The ventricles are more heavily muscled than the atria. They
must pump the blood to the lungs and throughout the rest of the body.
The heart beats on its own, thanks to its natural pacemaker.
This small cluster of specialized cells is called the sinoatrial node (S-A node).
It is located in the right atrium, the upper right room of your heart. The S-A
node produces electrical signals at regular intervals and sends them through
a pathway in the heart muscle. These signals cause the parts of the heart to
tighten, or contract. The heart's regular rhythmic contractions form heartbeats
and can be felt as your pulse.
The S-A node signals follow a natural electrical pathway that
helps the heart beat efficiently. An electrical impulse travels from the S-A
node through the atrioventricular node (A-V node), a second cluster of cells
located near the center of the heart. The A-V node then sends the signals out
to the walls of the ventricles.
Normally, the two ventricles contract a fraction of a second
after they have been filled with blood from an atrial contraction. This timing
sequence is called atrio-ventricular synchrony (A-V synchrony). It is very important
to the heart's work as an efficient pump.
When it is working properly, your heart's electrical system
automatically responds to the body's varying need for oxygen. It speeds up the
heart rate when you are climbing stairs, for example, and slows it down when
Sometimes things go wrong in the heart's electrical system.
The heartbeat becomes irregular or changes its rate inappropriately. This is
called an arrhythmia. An arrhythmia can occur when:
The heart's natural pacemaker develops an abnormal rate
The normal electrical pathway is interrupted
Another part of the heart tries to take over as the pacemaker
Though there are different types of arrhythmias, they all
have one thing in common: they may prevent the heart from pumping enough blood
to meet your body's needs.