The NY Heart Center performs thousands of electrocardiograms every year. An electrocardiogram is a recording of the electrical activity of your heart. The heart is made of many muscle fibers. The squeezing or pumping of your heart is the result of contracting and relaxing of these muscle fibers. The stimulus for your heart to pump is caused by electrical impulses. These electrical signals generate a pattern on the EKG printout. Your physician then analyzes this pattern to tell whether your heart is normal or experiencing stress, strain, or damage.