Abstract: Many studies have suggested that the atrioventricular node(AVN)can blockexcess or early premature atrial impulses and prevent from the ventricular fibrillation.This function is termed filtering property(FP)of the AVN.The aims of this study were to investigate the site of the functional A-Vblock(FAVB)and FP of the atrioventricular conduction tissues in the rabbit heart in situ by means of programmed atrial stimulation,rapid atrial pacing,recording of the His-bundle electrogram and treatment with propranolol.We found that the FAVB occurred mainly at the His-Purkinje system(HPS).The results indicate that the AVN of the in situ rabbit heart may not have FPwhile the HPScan prevent to a certain extent excess or earlier supraventricular impulses from exciting the ventricle.

Key words: atrioventricular node, refractory period, filtering properties, rabbit