In 27 children (14 juvenile hypertonics and 13 healthy control children, with the mean age 14.7 +/- 0.4 y. or 15.2 +/- 0.5 y., respectively, P greater than 0.05) the changes of heart rate (HR), its variability (HRV) during deep inspiration and subsequent expiration, Valsalva\'s maneuver, doubled breathing frequency and the deepening of breathing were studied. The resting supine mean HR was significantly higher (P less than 0.001) in hypertonics than in controls. Deep inspiration was in both groups accompanied with the HR increase. However, the percentage increase in hypertonics was significantly lower than in normals (P less than 0.02). With subsequent expiration, the HR fell in both groups. There was no significant difference between the percentage decreases in both groups (P greater than 0.05). During the Valsalva\'s maneuver, in the first phase the tachycardic response occurred, which was in hypertonics significantly less pronounced. After the recovery of breathing a bradycardic reaction occurred which was equal in both groups (P greater than 0.05). Both, in juvenile hypertonics and in controls the doubled frequency of breathing increased the mean HR and decreased the HRV. During the deepened breathing there was an increase in mean HR in both groups, and only in the controls there was an increase in HRV. Heart rate variability in hypertonics was lower than in the controls under all the conditions.