Transcutaneous electrical nerve stimulation (TENS) is generally used in controlling pain. Side effects are not frequent, but sometimes do happen. Among these, automatic disturbances have been described. The purpose of the investigation was to study high frequency TENS effects on heart rate variability and the plethysmographic wave. Results showed no change in heart rate variability parameters (Standard Deviation, Mean Square Successive Difference) despite an increase in R-R interval, while a decrease in the amplitude of the plethysmographic wave was observed. This study seems to point out that high frequency TENS does not modify the neural control to the heart while a sympathominetic effect is shown on the peripheral plethysmographic wave.