Abstract: "Electrocardiogram of six leads including I , H , I .aVL.aVR and aVF was recorded and analysed in 180 Beagle canines at different ages. It was found that there was definite difference in heart rate ,P —R interval and Q —T interval for different age. Heart rate was slower,P — R and Q —T intervals were longer in older canines than those in younger canines, but there wasn’t obvious difference in QRS interval. "