The characteristics of cardiac activity in 5–7-year-old children were studied at rest and during graded veloergometric exercise. The indices of central hemodynamics strongly correlated at rest and the closest correlations were in girls compared to boys. Minute volume increased with an increasing load (from 0.5 to 1.5 W/kg) which could be attributed to an increase in stroke volume. In the groups of 5- to 7-year-old boys and 7-year-old girls the stroke volume increased with an increasing load reaching a maximum at 1.5 W/kg. In the groups of 6-year-old boys and 5-year-old girls the stroke volume increased up to a load of 1.0 W/kg. Heart rate represents another mechanism of cardiac output regulation. The chronotropic response to physical exercise in 5- to 7-year-old children was found to be sex specific, which was especially pronounced at the loads of 1.0 and 1.5 W/kg. Sex difference in the chronotropic heart response to graded physical exercise appeared at the age of 5, and the difference in inotropic response at the age of 7 years substantiates the heterochronous development of chrono- and inotropic cardiac functions.
