An electrocardiogram records the electrical signals in the heart. During an ECG, sensors (electrodes) that can detect the electrical activity of heart are attached to the chest and limbs.
These sensors are usually left on for just a few minutes. An ECG shows heart rate and rhythm, and can show evidence of a heart attack. It takes 10 - 15 mins and no preparation is required.
A standard ECG can record an abnormal heart rhythm only if it happens during the test. Some abnormal heart rhythms come and go, so a different type of heart rhythm monitoring, such as with a Holter monitor may be recommended to you.