Hostility and optimism have been shown to predict coronary heart disease risk. Salmoirago-Blotcher et al. used data from the Women's Health Initiative to examine the role of heart rate variability in explaining this association. Heart rate variability was inversely associated with hostility, but not with optimism. Although heart rate variability was associated with higher risk of coronary heart disease, its role in explaining the association between these traits and coronary risk remains to be determined.