During 1996-1998 (from March up to December 1998) this study was undertaken on cattle referred to large animal hospital of veterinary college, Urmia University. Electrocardiograms were recorded from 310 cases. The cattle were mainly crossbred (Holstein & Native ) and few Holstein, Brown Sss and native breed. 15 cases out of 310 cases (4.8 %) A - V blocks were diagnosed: 11 out of 15 cases (73.3%) showed first degree A- V block , 3 cases (20% ) second degree A-V block and one cases (6.6%) third degree A-V block. It was concluded that the first degree A-V block is mainly due to increased vagus tone. But second and third degree A-V blocks may accompanies in trinsic hear disease.
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