is defined as a heart rate
below 60 beats per minute. So, by definition, your nephew has bradycardia. Some people (often athletes) have heart rates this slow normally. Bradycardias can also be caused by abnormalities in the heart's conduction system.
Electrocardiograms are often done to diagnose the particular type of rhythm that is associated with the slow heart rate. Some of these rhythms are benign and unless your nephew was having symptoms (fainting
, shortness of breath
, chest pain
, etc.), he would not receive treatment for them. Other rhythms can be more concerning and will require a pacemaker.