Introduction: Despite extensive studies about effects of Crataegus monogyna on cardiovascular diseases yet, a few study has been undertaken antiarrhythmic property of this plant. Aims of the present study were: 1) To determine the protective role of methanolic extract of C.monogyna on the rate-dependent model and the concealed conduction . 2) To explore the role of Na⁺-K⁺ A TP_ase in the protective role of C.monogyna.

Methods: In all experiments were used of male New Zealand rabbits (1.5-2kg). Stimulation protocols were used to measure basic and rate-dependent ( recovery, atrial fibrilation and zone of concealment ) AV nodal properties in two groups(N=14) . In the first group all the stimulation protocols before and after different concentrations of C.monogyna extract were repeated (n=7) in the second group (n=7) in the presence of all stimulation protocols Ouabaine(0.05 m M) and extract were repeated. All results have been shown as Mean±SE.

Results: Basic and rate-dependent properties of node were inhibited after addition of plant extract of C.monogyna to KerebsHenselite solution . At the maximum concentration of cratagus.m(30 mg/l),WBCL cycle longth is increased significantly from 156.5±3.4 to 173±5.8 ms and nodal functional refractory is prolonged from 164.4±4.1 to 182.7±3.8 ms(P < 0.05).Was recorded Significant decreases of ventricular rhythm in both selective concentrations of plant. The depressent electrophysiologic effect of C.monogyna on the AV node did abolish inhibt by ouabaine.(Selective inhibitore Na⁺-K⁺ A TP_ase Enzyme ).

Conclusion: All results are indicating the potential anti-arrhythmic and protective effects of C.monogyna . The effect of plant in increasing nodal refractory period and widen concealment zone might be the major mechanism of this plant. The protective role of cratagus.m does not related to the Na⁺-K⁺ A TP_ase activity.