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SUMMARY : Understanding the underlying physiological mechanisms involved in sexual arousal is essential to treat effectively human female sexual dysfunction. Sexual arousal creates subjective feelings concomitant with genital and non-genital changes. The most common method of assessing female arousal over the last twenty five years is monitoring the vaginal haemodynamics using an inserted, free-dwelling photoplethysmograph and recording the blood-reflected infrared signals from the vaginal mucosa as the vaginal pulse amplitude (VPA) and the total blood volume (V.B.V.). Unfortunately, the signals are influenced by many factors, especially vaginal motility, and despite many studies the direct interpretation of these signals in terms of neurally-activated vaginal haemodynamics is still contentious especially in relation to vaginal blood flow during, at and after orgasm. Various authors have selected either VPA or VBV, or sometimes both, to interpret the haemodynamic changes of arousal but it appears prudent to reserve judgements about mechanisms until other confirmatory measures of vaginal blood flow can be utilised.