How the Heart Works

The average-size heart is approximately the size of your fist. It consists of the following:

• Two upper chambers (atria), which collect blood returning from the body and lungs and
• Two muscular lower chambers (ventricles) which pump blood from the heart to your lungs and body.

The atria are separated from the ventricles by valves which, when functioning normally, permit blood flow in one direction only. There are also heart valves that separate the ventricles from the large blood vessels transporting blood to your lungs (pulmonary artery) and the rest of your body (aorta).

Your heart also has a built-in electrical system that regulates the normal sequence of pumping to provide a continuous flow of blood through your heart to your lungs and body. The heart's own pacemaker is located in an area of the upper right atrium called the sinus node. This is the part of the electrical system that controls your heart rate. Electrical signals leave this area and move through pathways in the upper chambers, causing them to beat. There is an electrical relay station located in the middle of your heart called the AV node. Here, the signals pause for a split second before they continue their journey from the atria to the ventricles. In the ventricles, the electrical system is called the His-Purkinje system. It connects directly with the muscle in the ventricle and causes your heart to contract, or beat.