The heart is a beating muscle that pumps oxygen and nutrient rich blood throughout the body. Each beat is stimulated by electrical signals that pass through the heart muscle, or myocardium. In order to examine the function of the heart, a doctor may perform a test called an electrocardiogram or ECG (also referred to as an EKG). During this test, electrodes are placed on the chest and recordings are then made of the heart’s electrical signals. Sometimes the electrodes are also placed on the arms and legs. The electrical signals follow a set pathway through the heart beginning at a spot called the SA node, which is located in the top right chamber, or atrium. The signal then branches out through both right and left atria, which contract and push blood into the lower chambers, or ventricles. The electrical signal also passes into the ventricles via the AV node, and then travels down the tissue that separates these two lower chambers. Finally, the signal travels back up the ventricles, which contract and pump blood to the lungs and body. Variations from the normal electrical pattern may indicate damage to the heart due to a heart attack or heart disease. Often a patient will be required to perform a stress test during an ECG. A stress test usually involves walking or running on a treadmill at progressively increasing intensities while recording an ECG. This test allows a doctor to examine the heart’s electrical activity during the stress of exercise.
