The primary function of the heart is to pump oxygen-rich blood throughout the body. The oxygen is used by the body's tissues to perform their normal work. A by-product of this process is carbon dioxide; the blood carries this waste back to the heart and then into the lungs where it is expelled. The lungs also replenish the blood with oxygen. The oxygen-rich blood then returns to the heart and is again pumped throughout the body to meet the tissue's needs. A healthy heart will beat approximately 100,000 times each day and pump over 1,800 gallons of blood throughout the body's circulatory system.

Your heart is approximately the same size as your fist. Inside, the heart is divided into right and left sides by a thick muscular wall called a septum. The right and left sides are divided into upper chambers called the atria and lower chambers called the ventricles. The heart's right side (consisting of an atrium and a ventricle) receives blood from the body and sends the blood to the lungs where it is replenished with oxygen. After leaving the lungs, the blood travels into the left atrium and then through the left ventricle where it is pumped out to the rest of the body.

As you exercise or become excited, your body will demand more oxygen and the heart may pump more rapidly to accommodate this need. On the other hand, the heart will pump less frequently when your body is at rest (that is, when there is less demand for oxygen). The rate that your heart beats is normally controlled by an electrical impulse that originates in a small mass of muscle tissue within the upper right chamber of your heart. This specialized tissue is the sinoatrial node (or S-A node), the heart's "natural pacemaker". The S-A node will send an electrical signal through the heart's special conduction pathway (found in the atria and ventricles) that will cause the heart muscle to contract, thus pumping blood throughout the body. The normal heart rate ranges between 60 and 100 beats per minute.

From the SA node, the electrical impulse is relayed along the heart's conduction or wiring system. It spreads throughout both the right and left atria causing them to contract. The impulse also reaches the atrio-ventricular node. This special region transmits the heart's signal to the ventricles causing them to contract and pump blood.