The physiological response during diving reflex can be measured by recording standard physiological measures such as heart rate, blood pressure or skin conductance. Heart rate and its interpretation in terms of heart rate variability is becoming more frequently utilized to evaluate the balance between sympathetic and parasympathetic nervous system. Most frequently used is the frequency domain approach which allows differentiating specific frequency bands. The low frequency (LF) band groups the variability between 0.05-0.15Hz and is believed to represent the sympathetic cardiac control with slower unmyelinated nerve fibres while the high frequency (HF) band including frequencies between 0.15-0.4Hz reflects the parasympathetic or vagal control with faster myelinated nerve fibres (Berntson et al 1997).