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Changes of the heart autonomic balance between morning (8 to 9 h) and afternoon (14 - 15 h) measurements were studied in 22 healthy subjects. The selection of these two daytime periods was substantiated by the established higher risk of cardiovascular incidents in the morning and the relative balance of the vegetative nervous system in the afternoon hours. The changes were analyzed by RR-variability indices from ECG recordings in resting state and with vegetative nervous system stimulation by handgrip test and Valsalva maneuver. The authors introduced an indicator for time-related autonomic balance changes. The indicator evaluates the power of each RR-variability index to respond to changes in the autonomic control, in comparisons between resting state and stimulation data in the morning and afternoon measurements.