The electrocardiogram (ECG) is a simple, noninvasive test that is used to map the electrical activity of the heart. The test involves placing a total of 12 electrodes dispersed on the chest, arms, and legs that transmit electrical signals to a machine for analysis. A normal ECG typically shows a normal sinus rhythm with a heart rate between 60 and 100 beats per minute. ECGs are considered to be abnormal if the heart rate is slower (bradycardia) or faster (tachycardia) and/or shows a different rhythm. Examples include sinus bradycardia, ventricular tachycardia, atrial fibrillation, and Wolff-Parkinson-White syndrome. These arrhythmias can be lethal and may require emergency intervention like defibrillation.