Signals responsible for pacemaker oversensing may arise from the pacing system itself, P or T wave, concealed ventricular extrasystoles, skeletal muscle potentials, and distant electromagnetic fields. Oversensing is the most common cause of pacemaker pauses and a common clinical problem during follow-up of patients with implanted pulse generators. This article reviews the mechanisms and diagnosis of oversensing and the importance of multiprogrammability for its treatment.