Transesophageal atrial pacing was performed for evaluation sino-atrial node function in 102 normal children aged 2-15 years. These cases were evaluation again to make a controlled study after autonomic nerve blockade with propranolol(0.1mg/kg)and atropin(0.02mg/kg). In the group

values of SCL

SNRT

CSNRT

SNRTI declined significantly after autonomic blockade comparing with that before(P<0.01) .There was a highly positive correlation between SCL and SNRT(r = 0.8573 pre-medication and r = 0.8718 post-medication).Based on this fact

we suggest that SNRT = 1.15 SCL + 300ms(pre-medication)and SNRT = 1.56SCL ms (post-med-ication)be used as the equations to calculate normal value of SNRT in children.Because of the influence of autonomir nervous tension

it is nesessary to pace again following autonomic blockade administration for a definitive diagnosis of sick sinus syndrome