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How the Heart Works

A general understanding of how the heart works helps explain the different types of arrhythmias that can occur and how they might be treated.

Muscle
Chambers
Contractions
Electrical Pathway
Irregularities

Muscle

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.

Chambers

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.

Contractions

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.

Electrical Pathway

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 you sleep.

Irregularities

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 or rhythm
  • 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.