A Holter monitor is a continuous tape recording of a patient's EKG for 24 hours. Since it can be worn during the patient's regular daily activities, it helps the physician correlate symptoms of dizziness, palpitations or black outs. Since the recording covers 24 hours, Holter monitoring is much more likely to detect an abnormal heart rhythm when compared to the EKG which lasts less than a minute. It can also help evaluate the patient's EKG during episodes of chest pain, during which time there may be telltale changes to suggest reduced blood supply to the muscle of the left ventricle.