The cardiorespiratory plasticity in healthy children 9-10 years old (n = 72) was studied during the procedure of paced breathing. The observations of a child after an informed consent taken from him, his parents and teachers were carried out by a psychologist, a physiologist and a doctor after the lessons. In a preliminary series 1 minute trials of pace breathing with various frequencies (22-5.5 times/minute) were used which showed a good endurance of slow breathing. Inthemain series a 3 minute baseline recording and 4-5 periods of 1.5 minute duration with a stepwise reduction of breathing rate of 12, 8, 7, 6 times/minute and in 10 children - 5.5 times/minute were registered. Computer-aided pacer set the durations of inspiration, expiration, pause. The main parameters of heart-rate variability (HRV) and corresponding FFT spectra were analyzed by ANOVA. In children a high cardiorespiratory plasticity of heart rhythm according to frequency of pace breathing is observed. During the stepwise reduction of breathing rate a quasilinear growth of HRV and peak power of FFT spectra of RR-intervals are registered, reaching the maximum level in a HF-band at 12 breaths/min and in LF-band at frequencies of 6-5.5 that are critical to the sustained volitional control of cardiorespiratory processing in children. At 6-5.5 breaths/min a growth of HF-band power of heart rhythm modulation is also registered.