An electrocardiogram (EKG) is a test that produces a graphic picture of the electrical activity of the heartbeat. With each beat, an electrical impulse travels through the heart. The electrical impulse causes the muscle to contract and pump blood from the heart to the body.

Several sticky tabs called sensor electrodes are applied to the chest. These sensors pick up the electrical activity in the heart. The sensors are connected to wires called leads, which are then connected to an EKG machine, which measures how long the electrical wave takes to pass through the heart. This information helps determine if the electrical activity is normal or slow, fast or irregular. A new or old heart attack can also be identified by an EKG.