An electrocardiogram (EKG or ECG) is a test that checks for problems with the electrical activity of your heart. An EKG shows the heart's electrical activity as line tracings on paper. The spikes and dips in the tracings are called waves.The heart is a muscular pump made up of four chambers . The two upper chambers are called atria. The two lower chambers are called ventricles. A natural eletrical system causes the heart muscle to contract. This pumps blood through the heart to the lungs and the rest of the body.