The advent of prolonged monitoring with the implanted loop recorders has revolutionized the quest for detection of elusive infrequent arrhythmias in patients with unexplained syncope. The capability of prolonged monitoring has permitted us to obtain symptom rhythm correlation in the majority of patients suspected to have underlying infrequent arrhythmia. The implanted loop recorder is easily implanted in the left pectoral region with a minimally invasive procedure, providing at least 14 months of continuous monitoring that is both patient and automatically activated. Several recent studies suggest that it plays a major role in patients with infrequent symptoms and suspected arrhythmia, including patients with syncope and conduction disturbances, mild to moderate underlying heart disease, and atypical epilepsy. In a randomized trial, the device was found to be cost-effective and improved diagnostic yield compared to conventional tilt and electrophysiological testing. Wider application of prolonged monitoring is ongoing, including assessment of ventricular arrhythmias, atrial fibrillation, and conduction disturbances. The implantable loop recorder is most useful in patients with infrequent unexplained syncope when noninvasive testing is negative.