Long-term exercise induces cardiac remodelling known as exercise-induced ventricle hypertrophy and accompanied by electrical remodelling that can be recorded by ECG. This study aimed at recognizing electrocardiographic changes in rats undergoing long-term high-intensity interval exercise followed by a period of detraining. This study conducted at the Laboratory of the Biochemistry and Molecular Biology Department, FMUI from November 2014-January 2015. Four groups of young adults male wistar rats (100-200gBW) were randomly selected. Group 1 and 2 were assigned as control group for ECG recording on week (4 and 8) and (12 and 16) respectively. Group 3 was given 4 weeks of intensive training, followed by 4 weeks of detraining, while group 4 was given 12 weeks of intensive training followed by 4 weeks of detraining. ECG examination was performed at the end of each period of training or detraining and compared to control group of the same period of age. P wave in the exercising group was significantly increased (p<0.05), PR interval was decreased in group 4 after detraining (p<0.05). QRS amplitude was increased although not significantly different compared to control group. However, a significant persistent prolonged QTc interval was observed in the exercising group (62.76+4.03 ms and 64.24+3.78 ms) compared to control group (48.88+2.15 ms and 47.33+3.43 ms). Detraining did not restore QTc interval (57.81+1.96 ms and 61.16+5.02 ms) vs (48.93+2.40 ms and 48.13+1.66 ms). In conclusion, cardiac remodelling after long-term high intensity interval training causes ventricular hypertrophy with persistent repolarization disturbances after a period of detraining, indicated by an increase in QRS amplitude and a significant prolonged QTc interval.