Abstract: Observations of changes in heart rate and cardiac rhythem on patients with sinus brady-cardia(SB)and sick sinus syndrome(SSS)by ambulatory ECG(AECG)have been done in our lab,after electrophysiology study and drug test.The results showed that:1.There are signicant differences in all criterias between SB and SSS.2.Patients with SSS are more apt to be complicated with cardiac arrhythmias than thoes with SB,according to the above men-tioned results,the diagnostic criteria were established in this paper.

Key words: sinus bradycardia, sick sinus syndrome, ambulatory electrocardiograph