Increasing parity is associated with an increased risk of ischemic heart disease (IHD) and stroke in women. This is likely attributed to biological responses of pregnancy. Male cells of presumed fetal origin are commonly present in women years after pregnancy-a phenomenon termed male origin microchimerism. Here, we investigated whether male origin microchimerism was associated with risk of IHD and ischemic stroke in women. We evaluated the association between male origin microchimerism and ischemic events in a cohort of 766 Danish women enrolled in the Diet, Cancer and Health cohort during 1993-1997 when aged 50-64 years. Of these, 545 (71.2%) tested positive for male origin microchimerism by targeting the Y-chromosome (DYS14) in women's blood. Multiple Cox regression models were used to report hazard ratios with 95% confidence intervals. We found male origin microchimerism was associated with a significantly reduced rate of IHD (HR=0.44, 95% CI: 0.23, 0.83), but not ischemic stroke (HR=0.80, 95% CI: 0.46, 1.41). Our findings show that microchimerism-positivity is associated with a lower rate of later IHD development in women. Although the underlying mechanisms are presently unknown, male origin microchimerism may be relevant in women's cardiovascular health. More studies are needed to confirm these findings.