In a cross-sectional epidemiologic study of schoolchildren aged 11-17 years, the cardiac work index at exercise was found to be higher in schoolchildren with arterial hypertension (AH) and excess body weight than in the control group. The duration of an exercise test was similar in the two groups. The higher cardiac work index at exercise may be explained by considerably higher systolic blood pressure in schoolchildren with AH and by higher heart rates in those with excess body weight.