An electrocardiogram or EKG is a test that measures the electrical activity of the heartbeat. With each beat, a harmless electrical impulse or wave travels through the heart. This wave causes the muscle to squeeze and pump blood from the heart. A normal heartbeat on EKG will show the timing of the top and lower chambers.

An EKG gives two important types of information. First, by measuring time intervals, a doctor can determine how long the electrical wave takes to pass through the heart. Finding out how long a wave takes to travel from one part of the heart to the next shows if the electrical activity is normal, slow, fast, or irregular. Second, by measuring the amount of electrical activity passing through the heart muscle, a cardiologist may be able to find out if parts of the heart are too large or overworked.