In an effort to elucidate the effect of physical training on the electrocardiographic amplitudes, QRS vector, axis and QRS vector amplitude, electrocardiograms were recorded before and 1, 5 and 10 minutes after 3 minute rebounder exercise in 23 healthy male students aged between 18 and 21 years in two groups of athletes and non-athletes. ECG amplitudes were measured from lead I, V₁ and V₅ and axis and amplitudes of QRS vectors were measured from lead I and III in frontal plane, from lead V₂ and lead V₆ in horizontal plane. The results obtained are summarized as follows. ECG amplitudes: The R wave amplitude was 23.38±1.14 mm in athletes which was higher than 17.91±2.00 mm in non-athletes. After exercise, the difference in two groups remained significant throughout the recovery period. The S wave amplitude was increased significantly, and the T wave amplitude was decreased in both groups after exercise. The P wave amplitude was increased in both groups after exercise, and it was lower in athletes than in non-athletes. The PQ segment amplitude was zero in athletes but negative in non-athletes than in the resting state. The J point amplitude was positive in resting state and was negative after exercise in both groups. J+0.08 sec point amplitude was also lowered after exercise, and it was higher in athletes than in non-athletes. Therefore the whole ST segment was proved to be decreased after exercise. The summated amplitude of R in V₅ plus S in V₁ was 38.74±2.71 mm in athletes which was higher than 32.82±2.90 mm in non-athletes. After exercise, it was also significantly higher in athletes than in non-athletes. Axis of QRS vector: In frontal plane, axis of QRS vector was 62.7±7.36˚ in athletes, it showed no significant difference between the two groups. In horizontal plane, axis of QRS vector was -23.5±7.2˚ in athletes which was significantly higher than -38.8±8.2˚ in non-athletes. After exercise, it was significantly higher than the resting state in both groups. Amplitude of QRS vector : In frontal plane, amplitude of QRS vector was 13.86±1.44 mm in athletes which was significantly higher than 9.62±0.97 mm in non-athletes. After exercise, it was also significantly higher in athletes than in non-athletes. In horizontal plane, amplitude of QRS vector was 19.82±2.10 mm in athletes which was significantly higher than 16.90±1.39 mm in non-athletes. After exercise, it was also significantly higher in athletes than in non-athletes. From the above, these results indicate that R wave amplitude in athletes was significantly higher than in non-athletes before and after exercise, and that the summated amplitude of R in V₅ plus S in V₁ in athletes was also 38.74±2.71 mm suggesting a left ventricular hypertrophy We should note that the PQ segment and ST segment amplitude were higher in athletes than in non-athletes, and they were decreased with exercise in both groups. In particular, the fact that amplitudes of QRS vector in frontal plane or in horizontal plane were significantly greater in athletes than in non-athletes may be an index in evaluating athletes.