In this study various electrocardiographic parameters were investigated in 100 normal German Shepherd dogs by using standard limb leads (I, II, III). Three hundred recorded lectrocardiograms were studied for heart rate, cardiac rhythm, ECG intervals, amplitudes, wave forms (P, QRS, T) and mean electrical axis. Results obtained from this study indicated that : The most common arrhythmias were sinus arrhythmia and wandering pacemaker. The mean of heart rate in lead II was significantly different in dogs under 12 months of age compared with dogs older than 12 months. However it was no signification difference between males and females in all leads. The mean heart rate in age group above 12 months was 111.5±2.34 per minute and in group under 12 months of age, it was 137.65±3.80 per minute (table 1). The shape of P wave in lead I was either iso-electric or positive but it was positive in leads II and III. The shape of QRS in all leads were very variable. The shape of T wave was variable, positive wave in leads II, III and in group above and under 12 months were significantly different than others. Eighty percent of the positive T wave related to group under 12 months of age. The mean electrical axis of QRS was not significantly different between groups above and under 12 months of age and between male and female dogs. The mean electrical axis of QRS complex was 81.97±1.87 degrees (Table 1). This study showed that the mean duration of P wave in lead II, between groups above and under 12 months of age were significantly different. This study revealed that the mean P-R interval in lead III between age groups above and under 12 months were significantly different. This is due to the fact that the heart rate in older is slower that in younger animals. Normal ranges and variations of P, QRS and T waves are presented in tables (2 to 4) and findings of duration and amplitude of ECG waves are give in tables (3 to 7).
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