The heart is a beating muscle that continually pumps blood to the rest of the body. What we commonly call a heartbeat is actually the rhythmic contraction of the heart's four chambers. Each heartbeat is stimulated by electrical signals that travel through a specific pathway in the heart. These signals can be tracked and recorded by an electrocardiogram or EKG. The heart's electrical signal begins at the sino-atrial node, or SA node, which is located in the top right chamber, or atrium. The signal then travels to both the right and left atria, causing them to contract and push blood into the lower chambers, or ventricles. The electrical signal continues into the ventricles via the atrioventricular node, or AV node, and then into the tissue that separates the ventricles through the bundle of His. The signal continues down the bundle of His and into the left and right bundle branches, located within the ventricles. When the signal reaches the ventricles, it causes the ventricles to contract and pump blood to the lungs and body, completing the heartbeat. This system functions as the body's own pacemaker and keeps the heart beating at a normal rate of 60 to 100 beats per minute. If the activity of this system is interrupted due to heart damage or other medical conditions, it can cause the heart to beat at an abnormal rate or with an irregular rhythm. Should this occur, blood flow to the brain and other parts of the body could be compromised.