In contrast to the older infant or child in whom arrhythmias are usually secondary to congenital heart disease, arrhythmias in the small, preterm infant are most commonly secondary to central nervous system immaturity or extrinsic causes. Bradycardia is the most common arrhythmia observed in this population. The staff involved in the care of these extremely fragile and usually complicated patients have to be aware of the possibility of other rhythm disturbances occurring in such patients; this will help recognition and appropriate management of the individual cases.