Objective:  Work stress is associated with an increased risk for cardiovascular disease (CVD). Exaggerated cardiovascular reactivity to work-related stressors or incomplete recovery after work is a proposed mechanism underlying this increase in risk. This study examined the effects of work stress on 24-hour profiles of the pre-ejection period (PEP), a measure of cardiac sympathetic activity, obtained from ambulatory measurement of the impedance cardiogram. Methods:  A total of 67 male white-collar workers (age 47.1 ± 5.2) underwent ambulatory monitoring on 2 workdays and 1 non-workday. Work stress was defined according to Siegrist’s model as 1) a combination of high effort and low reward at work (high imbalance) or 2) an exhaustive work-related coping style (high overcommitment). Results:  High overcommitment was associated with shorter absolute PEP levels during all periods on all 3 measurement days, reduced wake-to-sleep PEP differences and reduced PEP variability, as indexed by the SD. Conclusions:  Overcommitment to work was associated with an increase in basal sympathetic drive and a reduction in the dynamic range of cardiac sympathetic regulation. Both findings are compatible with the hypothesis that overcommitment induces β-receptor down-regulation. BP = blood pressure; BMI = body mass index; CVD = cardiovascular disease; ERI = effort-reward imbalance; HR = heart rate; ICG = impedance cardiograms; MANOVA = multivariate analysis of variance; PAI-1 = plasminogen activator inhibitor; PEP = pre-ejection period; SDPEP = SD pre-ejection period; VU-AMS = Vrije Universiteit Ambulatory Monitoring System; WHR = waist to hip ratio.