An electrocardiogram, known as an ECG or EKG, records a person’s heart rate and rhythm by measuring the electrical activity of the heart.

In a normal heartbeat an electrical signal starts near the top of the heart and spreads across it causing the heart to squeeze and pump blood throughout the body. By measuring these electrical impulses, a doctor can see if you are having or have had a heart attack, look for or monitor heart conditions, determine the cause of chest pain, breathing trouble, dizziness, irregular heart rate and other symptoms, check the health of your heart before surgery or monitor the effectiveness of medications or treatments.

During an electrocardiogram a doctor or nurse will apply patches, called electrodes, on your chest, arms and legs which are connected to the ECG machine. The machine measures your heart’s electrical activity and prints the results. An electrocardiogram is non-invasive—sometimes we have to shave a little chest hair to get the electrodes to stick!—and there is no specific preparation a patient must undergo.