The echocardiographic parameters were followed for 3 years in 15 boys aged 13 years on average, who were beginning competitive canoe race training, and were compared with the corresponding data on 17 boys of the same age who did not take part in sports. As compared to non-sporting boys the 13-year-old canoeist boys had a larger left ventricular end-diastolic diameter (46.13 +/- 4.64 mm vs 44.35 +/- 3.06 mm), a thicker left ventricular posterior wall (7.47 +/- 0.74 mm vs 6.47 +/- 1.18 mm) and particularly a thicker interventricular septum (8.33 +/- 1.18 mm vs 7.59 +/- 1.6 mm) just after they began sport, in spite of the fact there were no significant differences between the two groups in age, height, weight and body surface area. The preexisting difference in left ventricular hypertrophy between the two groups increased significantly during the 3-year follow-up period. The thickness of the left ventricular posterior wall in diastole increased to 9.20 +/- 1.01 mm vs 8.24 +/- 0.83 mm (p = 0.006), and that of the interventricular septum to 10.73 +/- 1.58 mm vs 9.59 +/- 1.18 (p = 0.025). The hypertrophic index and the left ventricular mass corresponded to the data given above (9.97 +/- 1.25 mm vs 8.91 +/- 0.94 mm, p = 0.01; and 261 +/- 50.7 g vs 202.83 +/- 45.8, p = 0.002, respectively). The canoeist boys had a slightly larger aortic root diameter at the beginning, and this difference increased and became more significant during the 3 years (29.4 +/- 2.39 mm vs 27.18 +/- 1.88 mm, p = 0.006). There were no significant differences between the two groups in the size of the left atrium, the fractional shortening of the left ventricle and the calculated ejection fraction and stroke volume.