An electrocardiogram (ECG or EKG) is a simple test that records the electrical activity of your heart. The ECG tracing is a series of waves that represent the electrical events in the heart. By carefully examining the sequence of electrical events on the ECG, doctors are able to diagnose arrhythmias.

Holter monitoring is a continuous recording of the ECG, usually for 24 hours, while the patient goes about his or her usual daily activities. This test is useful for diagnosing arrhythmias that may not appear during a resting ECG at the doctor's office.