OBJECTIVES: In women, variation in the incidence of myocardial infarction (MI) has been reported with phase of the menstrual cycle. Mental stress-induced rheological and haemodynamic perturbations have been implicated in the triggering of MI. This study examined cardiovascular reactions to mental stress across the menstrual cycle, as a factor contributing to the known variation between the menstrual cycle phases in MI incidence. METHODS: Rheological and haemodynamic activity during rest and a prolonged mental stress task were assessed in 12 women during the follicular and luteal phases of the menstrual cycle. RESULTS: The stress task increased haematocrit, colloid osmotic pressure, blood pressure and heart rate, and decreased heart rate variability and R-wave to pulse interval. However, there were no effects of menstrual phase on rheological or haemodynamic function at rest or in response to mental stress. There were also no moderating menstrual cycle effects for the rheological or haemodynamic reactions over time to this prolonged stress task. CONCLUSIONS: Our findings do not support the hypothesis that variations in reactions to mental stress can explain the reported variations in risk for MI across the menstrual cycle.