An intracardiac electrogram which records electrical potentials within the upper region of the right upper chamber of the heart that receives blood from the veins and forces it into the lower part of the heart that moves blood to the rest of the body, obtained by the introduction of electrodes high in the upper part of the heart near the sinus node or the small mass of specialized cardiac muscle fibers located in the back wall of the right upper space of the heart: The atrial electrogram is used in localizing conduction blocks or delays in the normal flow of electrical impulses which cause the heart to beat and diagnosing arrhythmias or abnormal rates or rhythms, of the heart.